Hi,
I know posts like this don't help much - but it does confirm that things can work. I have a Korg M3 and Virus TI2 both connected via USB on my iMac (first and second USB ports nearest the stand) and, using Logic Pro, I have had no issues since the last Virus AU update. I always hit the "Live" button when working with the Virus otherwise I get a noticeable lag.
regards,
Kieron.