I just bought the z5500. My first impression was, "what the hell? My 11-12 year old Altec Lansing ADA880 sounds better!" Was so disappointed and then started to fiddle with all the settings to try to improve the sound. But then I let it run in for a few hours, and then the sound started to get better. Goes to prove that it requires burn in and burn in is real.
Or maybe after a while I became immune to the bad quality! lol, but no, I believe it just needed burn in.
With regards to the bass being too loud, I didn't feel that at all, not because I'm a basshead. I think mine's the new version and that they took the feedback about the over empowering bass and reduced it. Why do I say that? because at some point I thought my bass was not working. I was like WTF! My sub woofer is not working, I'll need to RMA and put my head/ear next to the sound outlet by the side of the sub woofer (aiya, I don't know how to describe la), and then I could feel some air coming out, so I was like "ok ok .. it works. The sub woofer was a bit tight at the start. Took a long time to loosen up and sound better.
Then I bought a Compass Amp and Denon D2000 & Sennheiser HD650 headphones. I don't use my speakers anymore

... Can't stand the sound compared to the headphones. Like the speakers are making the songs worst! @.@ but need to listen to it when my ears can't take the headphones anymore @.@
BUT, conclusion is, today the z5500 sounds a lot better than it did during the first day. I run it through the Compass DAC/Amp via coaxial/rca. And it sounds better than my 12 year old Altec Lansing ADA880

Thank God.
That's what happen to me while using my new Altec VS3251. I think next time just going to invest in the real deal. What i mean is real home theater systems.