I’m also worried about how much of the harmonics in the music is LOST by the amp
I don’t want gross harmonic distortion, but don’t abuse or lose the precious harmonics in the virgin recording either.
Since you are specifically addressing amplifiers, you are correct to be worried.
Electromagnetic interference
(EMI) is the killer and it's wise to address it as best you can, both internally and externally.
Unused ports can act like antennas with direct paths to sensitive circuits, so that's one external source easily fixed with dummy shielding plugs. Since most equipment have AC supplies, that's the internal source. If you are willing to open the case, in most cases it can be resolved by fitting a grounded shield between the power supply and amplifying circuits.
As others have rightly mentioned, amplifiers are just the start and EMI / RFI should be addressed wherever possible. Shielding power cables can stop the EMI from radiating outside of the cables, so they are well worth considering. Since RFI (Radio Frequency Interference) is everywhere around us in the atmosphere, shield everything and connect it directly to a central earthing point, not the
equipment's case.
