But, has the topic kind of morphed into audible noise caused by amps? If so, would it make sense that one channel per speaker would solve this issue?
No.
The problem is that an amp amplifies everything in its input, as well as its generating own noise. So an amp with high gain is going to amplify any grunge in the input signal more than an amp with lower gain. [edit] (That's also why one generally wants higher signal levels, if possible; noise induced in the wires will be relatively constant, and thus there will be a lower ratio of it to signal if the signal level is higher.) [/edit] Add that to the amp's self-noise from the circuit and any mechanical noise (from humming transformers, etc.) and you have the three causes of amplifier noise.
If an amp has only one transformer does that eliminate Xtalk, or is the noise coming from somewhere else?
Any competent design will have inaudible crosstalk. (Many extreme "high end" designs are simply incompetent; one cannot generalize about them, because there are infinitely many ways to be incompetent!)
Consider that one common source of audible noise in amplifiers is transformer hum. Even some generally "good" amps, such as Sherbourns, more often than not have transformer hum. Transformer hum may not be an issue for people with degraded HF hearing acuity, mind.
For optimal performance, I think dedicated transformer for each channel is actually an inferior design choice to a big common supply.
Noise, discussed above, is the first reason.
The second reason is that when one considers the real power needs of music, one quickly realizes that peak demands are asymmetric: basically never will all channels be called upon to response to a large peak. So a PS that provides a large "common reservoir" is intuitively better-suited to the actual peak demands of real music than separate small transformers for each channel, where one channel cannot "borrow" from another.
Bob Carver was the first to market the idea of a PS that was big but perhaps less capable than all separate channels would need to simultaneously reproduce big peaks. And market it to the hilt he did. But the general annoyingness of Sideshow Bob aside, he was right.
