Interesting. I don't think that I've heard another emotiva owner make this same comment. Possibly the Marantz is just very warm and rolled off in the treble and it makes a good match for the he-4. I've owned one 70's era Marantz and it was certainly warm with dark treble. Not sure though.
Yeah that is probably it. But that's just me. Before I bought the Marantz, I auditioned a Rotel amp - which sounded clinical and bright. I get listening fatigue from that as well that's why I stuck with the Marantz and Denon.