Jimmy, do you know which firmware and kernel versions you are using? From the compatibility chart in Triode's thread on the squeezebox forum, it looks like those matter... I'm in the dark, myself, but want this to work given that it is my intended setup as well.
I am using the USB32 input of my Master 7 in my lounge with Audirvana+, Pure Music, Fidelia and Amarra(full version) on a Mac Mini running OSX without issues. All the software is the full registered versions.
It definately works Plug and Play on the Mac. Amarra seems the hardest software to get to run properly but it isnt usb32 related.
I also run a Master 7 USB32 under windows 7 Pro 32bit on a relatively low powered Q9650 cpu with 4GB of RAM in my kitchen (using JRiver and Foobar) and another Master 7 via usb32 in my bedroom under Windows 8 Pro 64bit on a fairly maxed out 3930k running JRiver/JPlay.
I have had no problems apart from the Windows 8 machine which required the new version of JPlay (5.1) to work properly in direct mode.