Pros: superb sound quality, sensible construction
Cons: no spectrum analyzer, no provisions for connecting an external EQ.
I bought mine refurbished from Ubid in November of 2000. It was a 1999 (1998?) model, there are now 3 more generations of H/K AVRs since then (AVR-55 is very similar to AVR-45 which is actually one generation younger as is AVR-65; then there were "hundreds" and, very recently, "hundred-and-tens"; if you're trying to make some sense in their model numbers this might help).
From what i could tell after having both AVR-45 and AVR-55 in my house and choosing between the two, there is not much difference between them, except for a little different front panel controls design (i liked the 55's controls better), plus AVR-55 has a cpl more ins/outs for some reason but they are not arranged as nicely on the back of the unit, while AVR-45's connectors laid out and labeled very nicely. AVR-45's remote control is also different (newer, "universal", with a "wheel", same as AVR-65's) which to me was the main difference to 45's advantage. However, i don't use remote all that much so i went with AVR-55 for some extra ins and (seemingly) better front panel controls layout. My preference of the 55's controls is very subjective since i found the controls on both units somewhat cryptic at first and had to consult the manual a couple of times before i could set the speakers to work correctly (in a 3-way configuration w/subwoofer).
Both models i had were made in China, bought refurbished from Ubid. For all the technical details go to the H/K's website and look for detailed PDFs with all the specs and pictures front and back. They also sell refurbished units through their online outlet store.
Now, i've read a lot of complaints about chinese H/Ks and you will be well advised to go to http://www.audioreview.com/ and check out the reviews there. Biggest complaints i've noticed were a very unresponsive Customer Service dept. and a huge backlog in warranty repairs. I didn't have any problems with my unit in 5 month of moderate (both volume-wise and duration-wise) use so i cannot tell anything about that. My friend who got the AVR-45 (the one i didn't choose) hasn't complained either.
Now, I'VE ONLY USED IT IN 3-WAY STEREO (l/r + subwoofer) OR REGULAR 2-WAY STEREO. I have no idea or care about dolby digital surround part and i never even tried it (and not going to). I am using it for: my computer, tape deck, CD player, synth -- strictly audio, no HT stuff. Most problems that ppl had with these amps had to do the DD part (i believe).
I find the amp to be quite powerful, it lists the true wattage with no tricks of adding up all channels (which is cheating since it doesn't work that way). My Dahlquist speakers that are rated at 90W RMS (150W MAX) can hardly handle it at high levels. The amp has plenty of power for ANY home application.
Sound is incredible and i am also using very good speakers known for high "transparency". Bass is unbelievable, a lot of clarity and no "mushing" of the mids... If i ever have any second thoughts (i think I've paid a bit too much being a Ubid newbie at the time) the sound quality makes me forget all the doubts in a second.
The things i wanted but no such luck: a built-in spectrum analyzer (the LCD screen has enough space for an analyzer but it is annoyingly almost-useless during operation as it shows only some basic info). Further, no provisions are made for attaching an external EQ (there is only a 2-band onboard). Come on already! How hard is that? i know i can use "tape monitor" in/out but it's taken by a tape deck already... I expected a classier design from H/K. Add to that wish list a second headphones jack and a separate volume control for the headphones and that would be my dream machine. Minor? i guess... The only REAL PROBLEM i found is when you insert the headphones during the song playback while keeping the speakers on (it's an option) you hear a loud pop and a split second interruption in the sound coming through the speakers. That is not a normal operation probably but it is still quite unpleasant.
Finally, the looks... It looks cool! Very classy design. Much better than any of that "modern design" crap coming from all those Pioneers, JVCs, Sonys, etc., lately (am I the only one who can't stand the looks of these monsters?) Well, this H/K is a real looker. That's why my wife loves it too!!! :-)