If you aren't absorbed into the tube vs solid state thing, just buy a larger 100W to 150W per channel solid state amp from a reputable audio brand and you should be okay. Even new NAD and Yamaha larger amps sound okay vs older amps from 20 years ago. A good 100W/ch amp will drive even lower sensitivity speakers. Class A/B generally sounds better for the money, due to the larger linear power supply. Usually lots of used integrated amps (preamp + amp together) for sale here which often offer larger output than receivers which can focus on features you may not need (bluetooth, airplay, etc). A $500 used integrated from the last few years would be much better sounding than a new $500 (entry level) denon receiver.
Brad