Issues with performance and RAM previews

Just did a major system upgrade from an iMac to a Mac Pro, and now I'm having an issue with performance...specifically with RAM previews.

When I try to do a RAM preview with audio, it grinds my entire OS to a hault (can't switch apps, or click on much of anything). It eventually clears up enough for me to stop the RAM preview.

So, I'm wondering if maybe my Memory & Multiprocessing settings might be off.

Here are my system specs:

Mac Pro

2 x 2.4GHz 6-Core Intel Xeon (12 cores)

64GB RAM

ATI Radeon HD 5870

AE CS6 (11.0.2.11)

AE is installed on an SSD drive and the scratch disk is an internal HDD.

Here are my AE Memory Settings:

Here's my GPU Info:

Let me know if any other info is needed...