Greg, welcome. All competently designed amplifiers, certainly including even older Denons, are ruler-flat in their frequency response in the treble, so you can be assured that any lack of details in the upper frequencies isn't due to that. The M50 uses the same tweeter as the other Axioms and in the treble range above the crossover point there's very little difference between them, with each supplying plenty of treble(if it's in the program material). It may be that you simply want more treble than a speaker with accurate response delivers. Have you tried increasing the treble tone control?
