Logic Studios a bit cheaper than FCS
Compressor is also included with Logic Studio - which is a bit cheaper. I've had some compatibility issues with the AC3 files produced - couldn't import them to toast, for example. It wasn't a big issue for me so I never bothered sorting it all out. Hopefully Compressor is not simply included with Logic Studio for collaboration purposes, requiring DVD studio (part of FCS) to actually make the final product. You'll find lots of entry level stereo AC3 compressors (toast includes one), but you may find surround more tricky. Good luck.