Glare is normally used for extreme form of hardness or grain in the treble. So I guess one could say going from bad to good glare, grainy, hard, bright, smooth, dark.
Distinguishing it from detail is tricky as a brighter sound is easy to confuse it with more detail resolution. Indeed, truly more transparency, does sound brighter. So you have to be very careful, and I have been caught out in the past. One way of recognising it is with timbre - it the extra brightness is noise floor modulation for example, then all instruments will sound brighter - even those that are supposed to sound rich and dark. But if the brightness is better detail resolution, then smooth instruments will just sound clearer, not brighter. Also, if instrument separation and focus is worse, then it is not more transparency.
When somebody says it sounds better, but can't actually describe in details what the differences are, be warned! They may be preferring distortion. Fortunately, our lizard brain ignores all this - if its really better, it will be more emotional and involving, so you should use this as your goal. But assessing whether its more emotional or musical takes a lot of time, you can't do it on a quick AB test.
The USB filter devices help (hopefully) but do not solve the problem. It has to use galvanic isolation to do it properly.
Rob