Have you tried using the Adaptive Control Smoothing? See page 129 of the Virus TI User Manual.
http://www.virus.info/api/download/dlid/214/alternate/0/User manual Virus TI (series 1) in English
Right from the very beginning, Access have been applying a technique called “Adaptive Control Smoothing” (ACS) in all their synthesizer models, thus avoiding the zipper noise that rapid changes (knob movements, modulation) would otherwise cause.
> Off: Smoothing is disabled. Pros: Value jumps are immediate, with no glitches. Useful for gater-effects etc. when using a sequencer. Cons: Continuous control changes are incremental, meaning you may have to accept some zipper noise.
> On: Smoothing is enabled. Pros: Continuous control changes are smooth, so this setting is generally the better option. Cons: Sometimes too slow for intentional rapid jumps e.g. gater-effects.
> Auto: Control changes are analysed, and smoothing is switched on or off depending upon how fast these changes are. Pros: Smooth and sudden control changes can be applied to the same sound. Cons: Rapidly repeating jumps may be too fast to analyse correctly.
> Note: Smoothing is disabled, any changes are only heard at the start of each played note (not inbetween). Pros: No glitches. Cons: Smooth transitions not possible.
> Quantize 1/64 ... 1/1: Smoothing is disabled, any changes only occur at rhythmic intervals relative to the Tempo, expressed as a 4/4 bar division. See “Tempo” on page 129.