Hi there, the Virus is not necessarily a trance machine, even though it can do those sounds well.
It's an extremely capable synth, and tends to have a darker, smooth, lush sound to it. Anything from epic/atmospheric film stuff, special effects, ambient, distorted/distressed, plucky, LFO/arpeggiated, evolving paddy goodness.
The effects are pretty good, very smooth, and you can use these, as well as using the internal Virus filters, to process incoming external audio (a stereo audio input, accessing the filters and effects, would use just 2 voices). And this structure is all available per part.
Effects wise you have chorus, phaser, distortion, and a little so-called analogue boost, which you can use all at the same time, and on the Virus B you additionally have reverb
or delay (you can't use reverb
and delay at the same time, although you can fake it to a degree).
And, yes, in MultiMode you can use the Virus sounds with effects on one 'part', while routing an external input to process with other effects on another part. You can have up to 16 parts, but obviously due to polyphony (24 voices on Virus B engine) you can't hit anywhere near that figure in practice.
The difference between the Virus B and C is that the C has additional Moog emulated filters (with selectable 1-6 poles), so if you wished to also use the Virus for its filters it may be an aspect you want to take into account. The effects are the same, other than the C has a 3-band EQ with parametric mid, per part. The Virus C also has 32 voices of polyphony.