I know there was a thread on this several years ago, but the basic question I have was not covered. Other than the obvious differences between these two classic amps (output power, controls on the front, connections on the back, etc.), is one better than the other in terms of the internals? I know the design of these two is different as I have looked at the circuit diagrams, but what I can not tell, is one a better design than the other and/or did one use better components than the other? By better I mean better sound quality and/or less problems/less likely to fail/easier to maintain. I've heard both amps played through the same set of speakers and did not hear a noticeable difference. I don't want to assume that just because the 9100 was TOTL in its day, that means it is a "better" amp. For reference I have an 8100 that I've been repairing and I think the sound is wonderful. I picked up a 9100, but it has issues (protection, constant low level background hum and hiss), and I don't hear a difference in the sound quality (other than the hum/hiss issue). I'm wondering if it is worth keeping the 9100 or returning since the price was on the high end of what they seem to go for. Thanks for any opinions.