As you know I can be very stubborn in my beliefs. Just for laughs, I tried using metal film resistors everywhere that touches the audio opamp of my Echo (I also abandoned the DC-offset-correction resistors that were not really necessary, and that helped a huge amount, too). Sure enough, about 70-80% of the noise was gone. Yeah; the tone is a bit more on the clear side and a bit less soupy, but the noise was really bugging the hell out of me. I haven't yet proto'd the non-inverting opamp idea; but I just wanted to let you know I got a lot of mileage out of the metal flims already.
Thanks for the chat! Looking forward to hanging out with you sometime in the future...