I’m also worried about how much of the harmonics in the music is LOST by the amp?

To get high S/N and low THD you need to add quite bit of dB of negative feedback to the circuit. 
This reduces the second harmonic and increases IMD…leaving you with a harsh and sterile sound, stripped of harmonics.  
So basically what I’m saying is you may need a poor measuring tube amp if you want harmonic richness without transistor distortion. 

+1 atmasphere
Amplifier design guru Nelson Pass tinkers with harmonics sometimes adding more to his amp designs to get a pleasing sound.

If you are talking First Watt agree 100%. Pass Labs? Not so much.