would using a external midi/audio usb card disable the virus
 

ive been considering getting another synth and connecting it with a usb connection from an external midi/audio usb soundcard, maybe the edirol ua-25 perhaps.
would doing this disable the virus ti midi and audio input and function as a soundcard as i would be effectively using two soundcards at once.

It should not affect it at all. You should see both the Virus and your other soundcard in your DAW.

it shouldn't. unless you have a really shitty soundcard and you USB ist stressed out by the amount of data.