I'm an early (too early ) adopter of Snow Leopard, and here's my experience with OS 3.0.5 so far.
I have already discussed this privately with Marc and Access support, I'm posting this here so that people know what to expect when they consider upgrading to 10.6 in a few weeks.
Summary : 10.6 is not supported with TI OS 3.0.5, but I was still able to use VC, and the Virus TI as my audio interface in Logic 9 almost normally !
There are limitations however : apparently you should have the Virus plugged-in at system startup to have it recognized.
And most importantly, it seems impossible to use the Virus as your audio interface with applications that don't allow you to pick an audio device, but just use the system default (e.g. iTunes).
The reason for this, is that the Virus isn't listed as an audio interface in the Audio/Midi Setup App, except if you force that app to run in 32-bit mode (see its properties in Finder). And even then, you still can't select it as your default output/input.
I should mention that I'm running Snow Leopard in 32-bit kernel mode (go to the "software" section in the system profiler app to check whether that's your case).
So it's not really that 3.0.5 is already 64-bit ready, it's just that 10.6 in 32-bit mode "tolerates" some 32-bit components of drivers to work (VC, since Logic 9 is 32-bit anyway, the CoreMidi and part of the CoreAudio driver)
In short : although it's not supported, in my own experience if you have another audio interface that is working under 10.6 already, and you are not using a 64-bit host sequencer (are there any on the Mac anyway ? Cubase ?), and you're ok with your Snow Leopard kernel running in 32-bit mode, then you can upgrade to 10.6 and use your TI with VC in the current 3.0.5 release.
Of course, this is not recommended by Access and is my own experience, YMMV ...