I have been using an AMR in my amp for about 2 weeks now, and also ordered one for my preamp, but unfortunately, it arrived DOA. Bonnie at Avatar was very accomodating, but will not have any more of the value I need 'til after CES.
Anyway, after listeming for two weeks, my initial impressions haven't changed very much. Changes are definately positive, but in my system, more of a specific change than an overall change. One member on this thread described the change he heard a few weeks ago, as I recall, as making the midrange more vivid. This is what I have experienced. The treble region seems no more or less extended, and I don't really notice a difference in the power or the definition of the bass region. What was plain to hear was a cetain clarity, or increased sense of vividness in the mids. This is in no way percieved as brightness. My McIntosh 2105, much as I love it, can fairly be faulted for a mild murkiness in the otherwise excellent mids, and this AMR fuse seems to have "fixed" a problem that I didn't know I had.
While I had heard amps that were more lively in the midrange, I had thought that I would have to give up the fullness I was accustomed to, but that is not the case.
The increase vividness, if I can call it that, seems to give voices better focus, and as a byproduct, reveal more nuance and detail. I don't notice any differences in the soundstage concerning width or height.
For $20.00 a piece, I can't see how anybody would lose by trying them. I look forward to getting the one for my pre.