You said, "They can adjust the levels of each instrument/performer, they can add effects that apply to only one of the instruments, and they can make the final product sound like a "hit album" rather than "the local rock band".
Ok, well being a songwriter, record producer and musician, I can tell you that today's methods of recording and making music sound like a "hit album" includes some crazed engineers driving digital signals to clipping levels and distortion (just draw a "hit song" up on your wav editing screen and watch the high and low end hit the limits.) They are trying to make Garbage sound hit-like. Unfortunately, this is the norm today .. the feeling of LOUD compressed music as opposed to lower levels and clear, low distortion recordings. Louder is commercially better, but is annoying as hell. A GOOD amplifer, and I mean very high end, handles the lower levels beautifully and enhances clear reproductive performances and mixes. A good engineer stays away from "hot" levels whenever possible. I could go on, but you catch my drift. BTW, I would prefer a high end Marantz, Quad Pioneer or McIntosh 70's vintage amplifier with floor standers housing 15" woofers anytime against the crap they make today ... I rebuilt my older system and it sounds awesome, reaching all of the frequencies flawlessly at almost any level, and without siginificant distortion. Playing digital tracks trough these old monsters is an awesome experience. I use a Pioneer 7 sound for rear speakers and the McIntosh Tube amp for the front stereo on movies. You won't need a high end sound card either, and the sound will blow you away.