Hi Spreader,
Fellow Snow user too
It's slightly obscure, away from the usual oscillator or effects stuff, it's located in the Common menu instead.
So Edit > Common (top-right most button), then scroll through the parameters (pages) until you see the 'Input Mode' menu option. There's three selections for this: Off, Static and Dynamic. To enable audio in, you'll want to choose either Static or Dynamic. If you want to use the Virus as a conventional effects box choose Static, as Dynamic mode is for gating the signal using MIDI instead.
For more information about the differences of Static and Dynamic, see here:
http://www.infekted.org/virus/showth...939#post302939
Once enabled (in Static or Dynamic mode), to the right of the Input Mode you can select which audio inputs you wish to inject into the Virus.
Now you can go to the effects and add whatever you want to the input. You can also use the standard Virus filters, resonance on the audio input too, and even use LFOs and stuff to modulate these.
To use a full stereo signal, make sure oscillator Unison has two voices selected. This enables the required two voices of polyphony to process both inputs.