Hi, I worked with GPO under ASIO and it worked great, but when I wanted to do a mixdown via VAC the timing got screwed up. Double checked and assigned the output to the MME driver of my RME Hammerfall DSP and yes, with MME there is really weird timing. I prepared an example: http://www.audionomio.de/mp3/GPO_Timing_with_MME.mp3
If you\'re using GPO Studio and choosing VAC as an MME audio output, then you could have troubles. Your latency will only be as good as the lowest MME buffer size you can achieve; latency is typically bad with MME compared to ASIO. Also jitter is worse with MME, so your timings are more likely to be suspicious. If at all possible, I\'d recommend using ASIO (on Windows) in GPO Studio.
I wish I could say more about VAC. We haven\'t done any testing with it, so I\'m not sure how well it would work under optimal conditions. If it\'s MME only and you wish to use it with GPO Studio, than unfortunately I have the feeling you won\'t get excellent results. You might achieve results that seem \"good enough\", but it would depend how demanding you are about latency and jitter. MME in GPO Studio won\'t really allow for low latency.