Ear is most sensitive to THD at higher frequencies. I'll let the guys that know fill in the blanks. Your ear is most insensitive at very low frequencies......which is why subs can get away with 5% distortion or whatever.....which, if it happened at 1000hz, would drive you from the room.
Don't worry about specs. Their is a relationship to feedback which some persons object to. Just for example, the Japanese amps of the 70s had amazingly low #s, but were high feedback designs. Again, the knowledgable ones will be along in a minute.
As for Emotiva? You could build the identical design of amp....#1 used all premium components, matched semiconductors, huge heatsinking on outputs, heavy gauge chassis, transformers it takes a forklift to move, and other 'quality' touches. MTBF is very high. Before being mass produced the piece was 'voiced' and sounded GOOD.
#2? Built with parts from Fry's or some catalogue. Just the values called out, with no matching, or thought of other characteristics of the part.....Caps have a resistive and an inductive component, for example. Everything else was built or sourced with price in mind. Meets specs? Sure. Sounds good, too....but not quite up to #1s level. More production variance and less lifetime. Sales price point?.....A heck of a lot lower than #1.
Just my opin.