I'll be honest. As of right now, I prefer the PLIIx applied to whatever signal coming across, even PCM 5.1 soundtracks. There just might be something to what's being talked about that the analogs should have bass management, etc or it may be just my equipment.
I compared spidey 3 raw PCM 5.1 over analogs to same pcm track over the optical connection which gets the PLIIx treatment as well as THX processing. Maybe it's the fact that the rear speakers (rear of 7.1) are being used. Anyway,it's a little surprising. They both sound great, but, I guess PLIIx and THX are doing their job.
Also, for anyone with a 720 native display, setting the output for 720p had much better results for me than taking the default of 1080i. This is on a Sony XBR 70in.
Latest impression of the player: THIS THING ROCKS! (no real problems, but, no Fox BD discs either). Tested Blu-ray, HD-DVDs, regular DVDs. Very smooth...