Hello, I use GPO + Sonar 4, and find the combination excellent.
I have 3 GB RAM, yet still need to convert the MIDI to Audio and layer the Audio. When I do conversions, the audio file always ends up with a certain amount of background hiss, and as I layer these audio tracks the hiss just compounds to an unacceptable degree.
Should I even be getting hiss off of a purely digital sequence? I have a SB Audigy 2 ZS soundcard, and wonder if I should be using something different, including external sound hardware. I've experimented with ASIO vs WDM drivers, as well as gain, recording settings, and have no mic installed.
When you use GPO, you should forget all about recording. GPO is best used as a VST plugin and to get audio from it, you "Export audio" (and maybe "Bounce to Track, I have not tried that yet). This process is purely digital and, to the best of my knowledge, does not involve your soundcard, so should not produce any hiss. If you "Export Audio" you just Import the audio track(s) afterwards. I would imagine "Bounce to tracks" does this automatically.