How to do this?

[Timo]

The audio inputs don't run through the oscillator and pitch stage. Only the filters, amplifiers, and the effects, etc.

However you could fake pitch modulation by running it through the Virus' chorus effect (using something like Dir/Eff = 127, Rate = 110, Depth = 127, Delay = 35, Feedback = 0, Shape = Sine). If you want a blend between the pitch effect and the original, just set Dir/Eff to your choice.

You can also go one further and set the audio input to dynamic mode (meaning you use the Virus keyboard as a gate/envelope for the incoming audio), and start using the modulation matrix to control the Chorus settings (along with any amp and filter envelope settings to be controlled via the Virus' keyboard).
If you get clever, you could also use the matrix to map amp-attack time to chorus wet/dry, for a fade-in of the pitch effect, etc.

Ideally, however, just use your ROMpler synth engine. I'm sure your orchestral VSTi would have been bundled with one, or you could dump the samples into a sampler VSTi (Kontakt, Halion, etc.)