Well, I don't have the 550 altho I do have an old 6.1 DE597 in my workshop (it got demoted due to no hdmi, use an Onkyo in my bedroom and a Denon in my living room). Sony doesn't get a lot of love in avr land these days in general, but I've found my unit basic and reliable and inexpensive...the reasons I bought it originally. Doesn't have much in the way of dsp/room eq type stuff and limited setup parameters, but it works fine. The audio quality is fine altho I do prefer my units that have more amp channels, hdmi and provide Audyssey room eq/auto setup functions.
Don't know about reliability issues reported, I don't remember reading any particularly, but keep in mind people come to the audio forums to complain more than praise and bad news always spreads faster to boot. If you like your setup that's what counts.
So no video or multi-ch content or? I don't see any added setup....