Yes and no. I've owned a "dedicated stereo system" in many guises - stereo receivers, integrated amps, separates, and mono blocks. The keys to evaluating a multi-channel amplifier vs. a dedicated stereo one are multitude.
If you have a auditorium-sized listening space and/or if you listen at rock concert levels and/or if your speakers are low-impedance/difficult-to-drive, then one is unlikely to get equivalent stereo out of a multi-channel device of most varieties.
If, however, like me, you have a more modest room, listen at more modest levels, and have relatively sensitive and easy-to-drive speakers, then I would suspect that you can get very good audio from a well-made and good-sounding multi channel source. In fact, you could get so close that in one of those mythical double-blind tests, I'd suspect that you couldn't really tell a difference.
This is pure heresy to high-end audiophiles, I know. We're invested heavily in the idea that consumer-grade audio is somehow inferior and can never rise to the lofty accuracy of our carriage-trade gear.
But the world has changed, and many of us don't yet realize it. Even the most cost-driven AVRs on the market know that they have to compete in the sound quality arena, or they won't sell. And when a company the size of Yamaha or Denon gets a sound-quality hit in a major magazine review, it gets their attention.
No, your $399 entry-level AVR won't now (and never will) compete with your Mark Levinson or even your McIntosh, but the entry level sounds better now than they've ever sounded before. And the improvements don't stop at the entry level, either.
"Midrange" brands like Rotel, Arcam, Emotiva, and others now provide a greater percentage of "cost no object" sound than they ever have. And that sound quality improvement spills over into AV gear too.
So I'd contend that SOME multi-channel amps, used within their power envelopes, with appropriate speakers DO rival the mono block or stereo-only amp sounds. Of course, this is my opinion, and you're always welcome to disagree.
Cheers - Boomzilla (moniker NOT indicative of listening preference)