Jafox: "So maybe it is only audible on certain music....or I am simply deaf!"
No, you're not deaf. Probably your listening skills are similar to mine--I can hear lots of differences but I definitely have a limit. Last fall, in a lengthy audition of interconnects, I could distinguish lots from others, but after some culling, those that passed all sounded the same--GREAT!
Each of us has a limit to our listeneing skills, and they're all different. Keep trying that signal-polarity switch; one of these days and recordings, you'll hear it.
One more point about preamp gain--linestages with high gain can create audible tube noise with high-gain poweramps. Understand that line stages amplify AFTER the volume control; that is, the volume control decreases the input voltage, not the output voltage, so the preamp's output noise is constant--unless a switch decreases it.
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