1) If your power amp has 6dB more gain that means you need to pad the input by 6dB or else you lose 6dB of s/n and dynamic range. That's gainstaging. Every pro is taught gainstaging pretty much from day one. Most audiophiles aren't pros, and have no idea how much their systems would actually benefit from being properly set up.
2) Op-amps aren't inherently balanced or unbalanced. An op-amp is simply a circuit - of any type, tube, transistor, or IC that uses feedback from the output to cancel distortion by inverting the feedback phase 180 degrees. The signal in is amplified and exits the amp amplified + distortion. A portion of that signal is fed back to the inverting input, passing through the amp resulting in the out of phase distortion canceling the in-phase distortion while the main signal isn't canceled.
Clever, except for the time it takes for the feedback to ... feedback.That limits the bandwidth of the clean signal. Fast transients that pass through the amp before the feedback result in 'transient intermodulation distortion' which occurs if the bandwidth isn't wide enough and the amp momentarily runs without feedback, resulting in all kinds of nasties. First Gen IC opamps like the 741 had very limited open loop bandwidth and as a result didn't - couldn't - sound very good. Modern IC opamps have long solved that, and several other issues and can sound very good indeed.
Avoiding single-ended inputs "to avoid opamps" is simply nonsense. The input stage of virtually every amplifier is an op-amp, of one topology or another. The very first opamps were AT&T long distance telephone repeaters, a vacuum tube design, in use a decade before the transistor, and 20 years before the IC were ever invented.
