Have just retried this since upgrading to the new Ubuntu release (10.4). Result: absolutely perfect so far. I'm stunned.
I did a fresh install of Ubuntu 10.4 and added the beta release of Wine. Installed Audiomulch 2.0.4 and so far every file I've opened has run and exported with no problems, VSTs included (maybe that surprised me the most). If that sounds simple, it was. The only configuration change I made in the entire process was setting the sounds device within AM to DirectSound.
Providing the rest of my tests succeed (have only done casual testing over a bunch of files so far) this gives the chance to finally fully move to Ubuntu for my home PC (only reason I have dual boot to Windows now is for doing music with Audiomulch).