You can notionally build as many stages as you want with a single amplifier, and AFAIR I have seen a 5 stage design implemented just to make the point BUT it becomes increasingly hard to "realise" (= construct) as you add stages around a single amplifier. To obtain the correct ratios of components requires increasingly precise component values and increasingly stable components. Capacitors are hard to get with extremely high precision and resistors are only slightly better. For a two stage or 3 stage design you can in most cases manage with 1% parts. Beyond that, the fun begins.
Note: "Pole" used generally here rather than saying "pole or zero as is applicable ..." in each case.
While you will notionally get the same result from a bandpass filter by cascading stages in any order, you will find that in limiting cases aspects such as stage Q and signal magnitude will have some effect. The same applies to stage order in a multiple stage low or high pass.
Your circuits are unusual in separately providing gain for the amplifier. This is acceptable, but the norm is to use a unity gain buffer in this application - amplifier Vout connected to amplifier inverting input. The addition of gain will also affect filter Q and you will end up not realising a classic filter polynomial if you alter the gain - assuming the designer implemented a 'proper' filter in the first place. In the case of the multipole design, varying the gain arbitrarily as shown will influence the "shape" of the resultant response rather than just its amplitude.
For one and two pole designs that need a unity gain buffer, you can use a 1 transistor emitter follower with usually acceptable results. As shown below, the results with a transistor with relatively low gain are inferior to results usually available from an opamp, but can still be very useful..
The above diagram is from this extremely good page -
Elliott Sound products: Active filters - Characteristics, Topologies, Examples
Lots more on the above, and related, here - Gargoyle search.
The two LPF stages you mention in your question - the 200 Hz crossover, and the output filter after the H bridge - serve different purposes, which should be distinguished from each other, you should avoid the temptation to 'compound' these into 1 by just making an output LPF with a cutoff frequency of 200 Hz. Let me explain why:
The 200 Hz low pass crossover filter serves the purpose of removing higher frequency audio content which your woofer cannot reproduce from your signal, and when used in combination with mid-high speakers with a corresponding high pass crossover filter, provides controlled transition between the frequency regions covered by the woofer and the mid-high speakers. The old-fashioned solution is a passive crossover, which sits in between the amplification stage and the loudspeaker and is made using large, high-power filter components, and in order to work properly the crossover needs to be incorporated in conjunction with a Zobel network - a further set of components which aim to compensate the frequency-dependent reactive part of the impedance and make the speaker appear as if it is a resistive load to the passive crossover - this is important for a controlled filter response, as a passive filter is loaded by the impedance attached to it which affects its response. The easy modern solution common in systems such as active speakers is an active crossover somewhere in the small-signal stage (prior to the amplification). As mentioned in the comment by @Majenko, a good option is to build this low-pass into the preamp, it can also come just after depending on your preamp circuit. I would not recommend having the low pass before the preamp, as for a good signal-to-noise ratio it is typically better to gain then attenuate, not the other way round, and also as a well-behaved audio input circuit has a high input impedance (e.g. 10 kOhm) which is flat within the audio band - something that a preamp circuit can provide but that a passive low pass on the input would not. You may also want to have a high pass here to block DC and very low frequencies.
The output filter after the H bridge, on the other side, serves the purpose of removing the switching frequency and all the PWM content, leaving just the desired signal. There is no choice other than to make an output filter passive - it has to appear after the switching stage, which means large filter components must be used, and it means that the filter is prone to the same loading problems as mentioned above for the passive crossovers. This is one common issue in Class D amplifier design - different loads cause different responses in the output filter, the unloaded filter has a sharp resonant peak which drops when the load impedance decreases, eventually reaching a point if the load impedance is very low when the transition between the filter passband and roll-off is so gradual that the frequency response in the desired range is affected - this is remedied in several architectures which use negative feedback after the output filter.
The load-dependence of the output filter is not such a problem if you ensure that the filter cutoff frequency is significantly higher than the highest frequency in the signal you are reproducing - this way, the filter won't affect the frequency response in your range of interest very much. So here is one immediate reason not to use your output filter as the crossover - otherwise, your PWM output will be reproducing higher frequency content in your signal which you will attempt to filter away with your output filter, which won't result in a controlled filter response - not only this, but you should not allow your PWM stage to output any signal at or near the filter resonance frequency, as at resonance the output filter (especially when unloaded) will present a very low impedance to the H bridge, and will draw high currents - potentially either blowing up your amp or engaging your overcurrent protection circuitry, if this is present.
Don't forget that the output filter cutoff frequency must also be significantly lower than the switching frequency to be effective. A general guideline to start you off is have the cutoff frequency about 10x (or more) lower than the switching frequency, (giving 20 dB attenuation at the switching frequency), and about 2x (or more) higher than the highest frequency in your signal. Applying this confines your output filter cutoff frequency to somewhere between 400 Hz - 3 kHz, which is plenty of room for play, quite a bit less confining than the typcal full-range audio Class D application. I would suggest you try to go for lower rather than higher within this little window, or as low as is practical given any restrictions on component size / price you have. This is because you don't need to go too much higher than 2x the maximum signal frequency for the load dependence to be negligible (provided that the characteristic impedance of your LC filer is not too high compared to the load), whereas the more attenuation you get at the switching frequency the better.
Hope this helps!
Best Answer
A low pass filter is pretty much defined by the R and the C value: -
\$f_C = \dfrac{1}{2\pi R C}\$
The same applies for a simple RC high pass filter and the steepness of the transition from "pas" to "reject" frequencies is very shallow: -
Even if the cut-off frequency did fluctuate by (say) 1% (and likely very slowly due to warming and cooling effects of the capacitor) the perceived change in tone would be minimal over that long period of time (at least several minutes.
Think about a slow 1dB change in volume - this could occur in a space of 2 seconds and you just wouldn't notice it let alone over a period greater than several minutes.
And there is certainly no dynamic effect of tone shifting due to the way the guitarist picks or strums the strings.
I don't think looking at CR filter changes is going to yield results that you think. I play and record guitar and have done so over many years. I do all sorts of things to the recorded guitar sound from basic equalization (messing with tone controls) to complicated effects and the least clearly obvious things that effect the sound of a guitar is movement of tone unless it is something dramatic like the wah-wah effect.