As a matter of fact, graphics can have a serious impact on performance, especially when you have a lot of floating windows with software and plug-ins not optimized for graphics performance. I quickly ran into this problem with my old MBP as it only had an integrated Intel HD GPU.
Anyway I'm pretty sure graphic card won't have any effect on it whatsoever, because graphic card is a matter of display
On my new machine, I disabled the graphics switching feature that would switch to the weak on-board GPU when the MBP feels it doesn't need the powerful GPU and can save some power. I have the power adapter plugged in most of the time anyways, and graphics performance shouldn't become the achilles heel with the powerful CPUs we can use today.
Seems like there's no graphics switching feature on iMacs, so that lead was wrong... if you're curious though, you can find out what card you're using by clicking Apple -> About this Mac -> More Info.
My OS is 10.7.5. I use 44.1 or 48kHz most of the time for my sample rate. My buffer setting i think is 1024 and honestly I have no idea what graphics card i'm using, haha.
Reinstalling the PLAY engine and iLok drivers might actually help - and it's easy to miss an update, EastWest's product support is very lacking and sometimes downright confusing. Double-check their downloads pages. Nevertheless, if that fails I'd write a mail to support. Might take them a few days to get back to you, be warned!
Sure my friend, hope I can help - I know how frustrating it can be to be hindered by technical obstacles like this. Rest assured, with a CPU/RAM behemoth like that sitting on your desktop, Logic really shouldn't be complaining even with 50 instances of PLAY @ 256 samples.
Your technical feedback is much more valuable to me than someone just listening to it, haha, so I appreciate what you've said so far. Thanks man!
Does it make a difference performance-wise if you use the Apogee's Core Audio driver?