I have been using old MC2100's amplifiers as monoblocks for quite a while with an MX118 as the preamp (stereo use only) and thought it was "that" time again to look at what had been going on and how I could, without spending big bucks (and not just change for changing's sake), improve on the sound that I liked so much. I came across a C45 and decided to try it "just to see"... I had bought the MX118 (used) because it was "all the money I had" at that time but it never deceived me. I knew it was not the best there was out there but grew accustomed to its sound and it really had been "doing the job" so far.
When I first heard the C45 with my set-up (I brought my amps and cables and the store had the same PMC's and Rega Apollo-R CD player in stock), I instantly knew that I would not leave the store without it. It really did improve the sound in almost all aspects - again, I know I did not have the best preamp (or amps) ever at home - but mainly, I don't know exactly how to call it, it improved in "presence". The room was filled with sound and it seemed that all the right sounds were at the right places. The silence's presence was also perfect (if that makes sense...). The store owner had me try different amps, "just in case" but I liked nothing as much as "my" set-up: the sound I knew and liked but now "++" with the C45!
As for the old MC2100's, as much as I tried, I could never get rid of them! Yes, newer stuff does have some improvement here and there (AND the Magical Blue Meters) but, at the same time, I find the newer amps to be less "forgiving" (and lacking the "love it or hate it" looks of the MC2100). And that's what I like so much about my amps. Now, with the C45 (unless I find a great deal on an MC452...) I'll be happy for quite a while. I can listen to almost anything knowing that bad recordings will still sound OKish but also that great recordings will sound even better. If you have an "ordinary" (even though no McIntosh gear can be called that) preamp, I greatly recommend that you have a listen to a C45 as, for the price they go by these days, they really are, in my opinion, a true steal.