Nfs – export the same folder with NFS and SMB

The issue

On my workplace, we have a rich environment of client including windows (from 95 to 8, also corresponding server editions), mac (from 10.6 to 10.8), linux (ubuntu, centos, redhat) and solaris.

Up until now, we have been exporting our shared files on our fileserver with both NFS and SMB, so that Windows can use SMB and everything else can use NFS.

Lately we have discovered that the way SMB and NFS lock files and set permissions on them are conflicting, causing a lot of lag and sometimes fails to provide write access.

What we've tried so far

• We've looked at QNAP NAS and FreeNAS to replace our fileserver, which is a simple Redhat linux box, however, relpies from our enquiries have informed us, that these services have the same issue.
• We've made a copy of the share that is mostly only read from (not written to), and exported one copy with NFS, the other with SMB, which works fine, but is really not a solution for the rest of our shares. We each mount our homefolders from the fileserver, and those tend to change alot, so having two copies would make for incosistencies.

Your solutions?

• We do have plenty of harddisk space on the fileserver, so keeping two copies of everything would be possible, but how would I ensure consistency between the copies? Can it be done with software? Or possibly with RAID?
• Is there a service that provides support for both of these protocols to work together? (like FreeNAS and QNAP didn't)

Is there anything I've left out, that I should have thought of? Any help or links to external resources would be very appreciated.