Nick, that's it: an amplifier, whether it's in a receiver or a separate unit, only has the job of increasing the incoming voltage(a gain of typically about 29dB, which is about 30 times)so that it's high enough to drive the speakers to an audible level. Competently designed units, which are available at quite low cost these days, don't add audible coloration, they just make things louder. The typical moderate cost receiver with a power rating somewhere in the 100 watt area not only handles the 1 watt or so used at an average loud listening level well, but for the vast majority of uses has plenty of headroom to handle brief peaks. Nothing more is required for transparent amplification.
