Computer speakers cheat way more I think.
0.75% THD is less noticeable than the 10% I saw one set of old computer speakers rated for. 10%.. I shudder to think what that sounds like.
The old integrated amp I now use is rated to, 30 wpc at 0.5% THD, and it sounds great. I can't notice a difference from my adcom, or HK, both with lower distortion and higher power ratings.
There's a lot of tricks manufacturers use. Receivers actually saying they're "not compatible" with 4 ohm speakers. That's like saying I'm "not compatible" with benchpressing 330 lbs. It has nothing to do with compatibility - I don't have the strength to do it. "incomaptible with 4 ohms" is the market friendly way of saying "we stuck too many amps into a small, cheap package so the quality took a nosedive" There's blatant lying on power ratings, since a lot of modern 5.1 receivers rate at low THD, and RMS, but give ratings of power that with a 32 lbs box, are very questionable.
I think brand reputation is a bit more important than specs now, because a lot of manufacturers treat specsheets like something they can lie on and get away with. Not that you should go out and buy a parasound halo or krell, but it doesn't hurt to buy a refurbished nad/rotel/HK, or from a company that'll always work with a 4 ohm load that doesn't lie about their power rating.
Back to the original topic.. how much wattage do you need? I guess it depends on that manufacturer's math. My amp is 30 wpc @ 8 ohms. This is with Marantz circa 1971 math, and it works well for me. A used 5.1 yamaha I had, rated at over 75 per channel, would go into current limiting and die with my thiels driving only two channels. That's with Yamaha, circa early 2000s math.
Modern power amps, rarely seem to lie about power. Some even rate conservatively, even cheaper ones, even 5 or 7 channel ones. The only place I can find where you get burned on specsheets is consumer level 5.1 receivers. The math used on modern consumer level 5.1 receivers is bunk for a large portion of them.
Math doesn't change much over time, besides audio electronics.
