BMXTRIX: Narrowing the question by stating that output of video would be through component and output of audio would be through 5.1 analog, would that cause you to modify your recommendations? Of course, that would leave out the PS3 and other players lacking analog outs, which brings up another question: If you already have a PS3, is there a worthwhile difference to be gained by switching to a player with analog outs?
Sorry, I'm not BMXTRIX, but I'd like a chance to chime in. I've had both the Sony 550 and the Panasonic 55. I stuck with the Panasonic for a couple of reasons. First, I don't know if they've fixed this or not, but the Sony 550 over analog audio while playing blu-ray...I never could get it to sound right compared to the Panasonic BD-10A I was replacing(No matter how I adjusted the multi-channel speaker set-up, I could never get adequate bass out of it).
Second, No frame by frame advance while the movie is paused. Pretty minor right? Not if you are trying to pinpoint something that just happened.
Third, I still have a large collection of dvd's which can be easily played over the optical/coax digital output from the player to my receiver, however on the Sony you have to make this change in the player's set-up menu everytime you switch from dvds to blu-rays as the player is not capable of outputting both bitstream over sp/dif and pcm via analog at the same time(no such limitation on my older Panasonic or the newer one).
Fourth, the Panasonic also plays divx media.
On the Sony's good side, it does look very nice cosmetically(certainly a more upscale look than the Panasonic) and it does include a 1GB usb drive to make it compliant with Profile 2.0 while Panasonic requires you to supply your own 1GB SD card to bring the player into Profile 2.0 compliance.
I understand this may sound a bit one-sided, but I also own a PS3 so I'm definately not a Sony hater and wanted more than anything to like the Sony 550, but in the end, it just wasn't good enough in my opinion.
Of course that brings me to your second question: Yes, there is a worthwhile difference between the audio from the PS3 via optical and a standalone capable of multi-channel analog output. Also, two minor additions to that. It's nice to be able to use my Harmony with my standalone blu-ray player and also, my PS3 sucks down 180 watts or so when playing a blu-ray move(more than my 46" LCD tv) while my Panasonic consumes no more than 30 watts when doing the same according to my kill-a-watt meter.