FWIW, I am really enjoying my combo of McIntosh C220 preamp (with Reissue Mullard tubes) and Odyssey Audio Stratos SS amp. The C220 does not have a theater bypass, but I just picked a set level on the volume control, and balanced my surround channels around it. Works fine. If you step up to the C2300 preamp, you get HT bypass. The Stratos is a powerful amp, and meets your requirements of being U.S.A. made, and on the slightly warm side of neutral. IMO, both are extremely well built and reliable, and both are produced by companies that firmly stand behind their products (even though one is a small direct-seller and the other a larger company with retail distributors).
Good luck!
Good luck!