What did I hear?

I'm new to this hobby and I'm in the process of trying to dial in a good audio system while remaining solvent, and also without driving my wife absolutely nuts.

Right now I stream digital music through microRendu -> Metrum Musette -> Quicksilver line stage -> Rotel 980BX -> Ohm Walsh Tall 1000's.  It's a pretty good system. 

I had the opportunity to borrow a friend's Mcintosh MA-5100, and swapped that in for the Quicksilver and the Rotel.  It was a dramatically different sound.  It was, for lack of a better word, tremendously more robust.  Not loud, but large.  Deeper bass.  Rounder tone, everything had more weight and presence.  Not in a distorted or in-your-face way, just, somehow... livelier.  Bigger.

Is that the fabled "McIntosh sound" that folks talk about?

I was actually surprised because the MA-5100 is a 45 watt amp, but it seemed to wake the Ohm Walsh Talls up more than the Rotel, which is (I think) 120 watts.  Plus, the Walsh's are not particularly sensitive, and by reputation prefer a high-current amp, which I would think was more like the Rotel, and less like the MA-5100.

So - how is it that what I *expected* to hear is so different than what I *did* hear?  Just trying to make sense of it all. 

I know the standard approach to stuff like this is to listen to everything and go with what your ears say, but I don't really have the budget, and my wife doesn't really have the patience, to swap gear in and out on a regular basis.  So I'm looking for feedback to help me understand the reasons for the difference I heard, so that I can make more informed choices about the things I *do* try.

Many thanks in advance for any replies, and also for the forum in general.  It's a great resource for people trying to educate themselves about audio.