I have a 54, and I have it bi-amped. I don't know the difference between the 53 and the 54, though I believe that the video bandwidth on the 53 is 50, while on the 54 it is 100. Not sure about that.
As to bi-amping... the sound quality is so subjective that it's tricky. While I think I hear some subtle differences, especially related to the low end, and an impression of being more solid-- more powerful; I also know how the mind plays tricks and we hear what we want to hear. Hate to sound wishy-washy, I guess I am saying that I am not sure that I could identify the difference between a bi-amped and a non-bi-amped 54 in a blind listening test. I can tell you this, it was incredibly easy to do, I didn't hear a loss or degradation in Sound quality. So while benefits may be imagined, I feel confident in stating that there isn't a loss.
Oh yeah, did I mention that I really like this receiver?! it rocks!
