If by "better sound" you mean better detail and much more dynamic than what you get with the Onkyo then yes, it will sound better. However you have to be careful with what you pair the 7500 with since it tends to lean on the bright side. I don't know if I'd add it to an Onkyo or Denon receiver either since their receivers used as pre-amps also lean on the bright side, especially Denon. If you are seriously in the market for an external amp I'd check out B&K's ST line for a good "bang for your buck" amp.
