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

Quads excel In the  mid range especially the older 57, but not in Bass or highs vs $$ speakers 
maggis I have owned a bunch cheap Xover parts,and frame is a disaster unless you buy a quality Mye stand  they flex like a sail
I am referring reference in a 3 way capacity when I am saying a retail speaker $15-20 k is average for a mid fi reference speaker 
by today’s $$ pricing standards when $100 k is considered upper end ,$50k mid reference ,which I cannot afford.sadly .

I'm not 100% certain but I think REW might be able to measure harmonics.

+1 mostly everyone- the entire audio chain matters

@redwoodaudio
If you’re after better sound, chasing harmonic numbers will not tell you if a component sounds good in your audio chain. Also, what sounds good is subjective- some folks like the warmth of tube gear while others seek a different kind sound. You have to use your ears.

Our hearing is much more complex than current science can measure. While good measurements can lead to good sound, good measurements does not equal good sound. You have to use your ears.

Perhaps it’s semantics but we don’t usually evaluate our systems on what we lost like “harmonics”, but rather how well it performs. You’ll likely hear better sound including harmonics on a more transparent audio chain which usually means more expensive components.

If you want to improve the sound of your audio chain, you need to make sure your speaker is revealing/transparent enough to hear what the components are doing upstream. Then you can change/upgrade components to move towards the sound you find most pleasing - by using your ears.

Cable quality plays a much bigger role than most realize