Hi Mr. D,
I apologize for not getting back to y'all earlier. I got caught up with some other stuff and just decided to order a Schiit SYS to see if that fixed the problem.
I was using a cheap FX Audio Tube pre-amp/buffer with the upgraded GE tubes. The tubes definitely produced a significant amount of noise once the volume knob hits the 9 o'clock mark, and the noise only increases from there on. I received my SYS yesterday and tried it out last night. With my chromecast audio and NEC cd player connected on the SYS, the noise on the speakers was cut down in maybe half. There is still a very faint shhh noise on the left speaker when I put my ear right next to the drivers, while the right speaker has a faint high pitched noise on top of the shhh noise. I'm only a beginner in audio stuff, so I would assume this would be what you call the noise floor of the amp, right? Now with the SYS, music is more detailed and has a very slightly wider soundstage compared to the FX Audio tube preamp. I tried connecting the chromecast audio to the FX Audio then routed the sound to the SYS before going into the amp, and the sound warmed up a tiny bit with a very minimal sacrifice in soundstage. So, based on the different combinations that I've done so far, the noise that I'm hearing is coming from, or caused by, the amp itself.
Last week, before ordering the SYS, I tried the amp plus FX Audio tube preamp on my daily system with NHT speakers. There was still that shhh noise and a slight high pitched noise (I don't exactly know the frequency of the noises). Although the noises that I'm hearing on my NHT's with the amp are similar to the noises that I'm hearing from my Pioneer stereo receivers and vintage integrated amps. I guess the noise floor is normal with such a high gain amp. Kindly correct me if I'm wrong.
Based on last night's listening session, I am happy with the amp. I will give it another go tonight to see if my thoughts change. Before getting this NuForce amp I had a Linn LK140 that I bought used, but decided to return it to seller because one channel was buzzing and when I opened it up there were signs of damage, repair, and a missing capacitor. That amp was quiet though, aside from the buzzing on one channel. My other amp option is to get another used Linn amp and hope I'd get lucky with a good example.
Thanks for your help, Mr. D, and to everyone on this forum! I really appreciate it.