Right, this one might be complicated to explain:
I just got hold of a 2nd hand Supernova 2 to help me remix some old tracks.
I've set Cubase up to have that unit configured as an external instrument.
If I use my RME Hammerfall Multiface's MIDI port, everything's fine.
Last night, I tried using the Virus' MIDI port to drive the Supernova and had the following problem:
When I put a plug-in with large latency on the master output strip (Powercore MD3), the timing of the Supernova was audibly way out when compared to a VSTi based drum track.
Removing MD3 improved things. Using the constrain PDC also improved things. Larger buffer sizes on the Hammerfall made things worse.
It seems like the Virus' MIDI port has some kind of offset or it's reporting back an incorrect latency to the PDC mechanism in Cubase.
Like I say - Hammerfall is fine in all the above scenarios.
I've probably already described the relevant kit above, but as for versions: Cubase 5.1 PC (Vista 32 bit, Service Pack 2), TIOS 3.1.0.0
It's not causing me immediate problems since I'll just use my other Hammerfall Multiface, but Access may want to look into this.