I know the virus C has a totally different engine to the Virus B. But is there a big difference in the sound quality? As in, is the virus C more bassier, dirtier etc.
With the 6.5 OS on the virus "C" you have an extensive filter bank including a 1, 2, 3, and 4 Pole filter also the virus "C" has a more compressive modulation matrix. 6 Sources, 9 Destinations vs Virus "B" which has 3 Sources, 6 Destinations also increased Polyphony in the Virus "C" vs "B" 8 more voices. Both 16 multitimbrality, the "C" has more simultaneous effects 16 more I think.
Also The New Virus Classic has pretty much the same specs as a Virus "B"
To answer your question: apart from the incremental features set of Virus C explained above, they are completely the same. The Virus C uses a faster DSP chip which allows more functions and polyphony, but the digital to analog converter are the same in the Virus b and c. So, the identical patches (those not using C features) will sound exactly the same!