I have to disagree here. I think in order to make a judgment about amplification it takes living with the different amps in a single system for a while. In other words, the only variable should be the amp(s). I don't think the differences are readily apparent unless there is a defect in the amp. However, there is no doubt in my mind that there are amps which will give you more smiles - more magical musical moments than other amps for a given time period. That's how I decide which amps to use for both HT and stereo.
For HT I use multiple 2 channel stereo amps anyway - except for one system which uses a PVA 5 Anthem 5 channel amp.
I think if you want a quickie, audition a nice well designed Single End Triode tube amplifier of 5 wpc or more like an Antique Sound Labs MG S1 15DT. It shouldn't take too long to realize that your smiles per unit of time rate has increased noticeably.
Nevertheless, I think JohnK is right when he says that the components which provide the most noticeable improvement are speakers and sources.
I got back an H.H. Scott stereomaster tube tuner, refurbished and very slightly tweaked - and the sound quality is truly amazing. I listened to some FM from a nice, well regarded solid state Denon tuner, and could never warm to the music. With the Scott, I cannot get enough of it.
I turn the glorious illuma-dial to KJAZ and enjoy the music at least as much as I do from the CDP.
Anyway, I've enjoyed everything from Parasound to Marantz to Yamaha M80s, Onkyo Integra M504 amps, and have settled on a few favorites which I will share unsolicited:
1. All time favorite: Antique Sound Labs MG S1 15 DT integrated KT88 5 wpc SET tube amp.
2. Kenwood KA9100, silver faced flagship from the 70s or 80s, 95 wpc. Love this amp!!
The rest are excellent, but they are merely all the rest ...
