I am using a Onkyo TX SR-707. My Sennheiser HD598's and my Klipsh S4 sound incredable through my Home reciever. So much better then my Ipod with a small E6 amp. Basicly I am wondering what kind of upgrade of sound will I get if I decide to go out and get a deticated Headphone amp. How much money will it take to plug a headphone amp in and be blown away over my current set up? Any suggestions on this would be greatly apprieciated.