It may help to add the make and model of your amplifier. Also, which Pi model?
Exactly how is your hardware interconnected?
Harman Kardon model number?
The Amp has no analog (RCA) or digital inputs (hdmi, optical or coax)? That's a first for me!
Does the Pi have an audio output besides hdmi?
Use an HDMI audio break-out box to extract stereo audio for RCA outputs; or perhaps S/PDIF if the Amp has a digital input.
But now I want the the analoge audio from the TV pass through the PI to the USB output of the PI.
My amplifier is only equipped with a USB connector.
So what you want is a high-quality A/D converter. I don't think going over RPi is the best solution, because it requires audio mixing.
I suggest to buy a USB audio interface.
