as the speakers are 8 ohms & 91db-efficient, and the sx-750 is 50wpc into 8 ohms, and will do 4 ohm loads no problem, it will be more than sufficient. sure, you can get more power, but unless you have a huge room and want sustained spl's >110db, it probably isn't necessary.
since the word on the street is that the sx-750's amp is similarly spec'd out as the more mondo pioneer receivers, except lower power, i m not sure if you would get noticeably better sound quality moving up the line. but, as you move up the line, the tuners will better. i really don't know the details; you would have to do a websearch for the detailed specs. and, if you move up the line, (or get an older similarly powered but top-line model like the sx-828), you will have preamp outs/main inputs, which is a nice feature, if you want to ad a processor, or crossover and a second amp for subwoofers, for example. if you want an sx-1980, be prepared to spend up to $2k for one in proper shape. if you really want a pioneer, and want a top model, consider the sx1250 - it will still be expensive, but no where near the cost of a 1980, and it will still have way more power than you will ever need.
these are fine receivers, for sure, but do not forget the likes of sansui (especially their integrated amps), kenwood, marantz, yamaha and harman kardon. and, less popular in the receiver realm, but still excellent - sony, luxman, nakamichi...
you should really research what's important to you, and what aesthetics you are wanting.
doug s.
