Just a suggestion, but have you tried isolating the inputs to see if that affects the hiss? Just wondering if it might be coming through from one of your components, even if it's not selected on the TGP. I had a problem with my Sat. receiver connection. In my case the noise was being introduced from a coax cable, and was present even if the Sat input was not selected. With the coax from the antenna disconnected from the Sat receiver, noise went away. Anyway, just a thought. I'm sure you already know this, but it never hurts to repeat it. Be sure to turn everything off before you plug, or un-pluging any connectors.
Sunfire: Theater Grand IV, Cinema Grand Signature.
Carver: TFM-45, PST-24 Cassette, Extra Carver Gear: CT-6, C-11 (S/N 00001).
Polk Audio: Mains SRS 2.1TL, Center CSiA6, Surrounds FXiA6 and FXiA4, Sub DSW MicroPro 1000, Extra Speakers SDA 2A, SDA 2Btl, Monitor 10A.
Turntable: Dual CS 714Q
Bluray/SACD: Oppo BDP 83SE
CD: Sony 330 300 Disk changerhttp://www.douglasconnection.com