I have some hearing loss too - I'm 69. I can't hear above 10kHz and I'm down in the 6-8kHz range, and one ear doesn't seem to hear 7kHz. I've no idea if this is typical. I read somewhere that in some cases this hearing damage can cause harshness in some frequencies (I don't know the source).
I've made a great deal of effort to set up my speakers and listening position in my dedicated room and used copious amounts of room treatment as well as EQ. During the process there were times when I couldn't hear certain percussion that I knew was there from headphone listening and also if I went closer to the speakers. Eventually I got it mostly right. I should add that recordings can be inconsistent too. I have to say though that I rarely hear really good percussion on the mostly studio recordings I listen to (of pop music, mostly country/folk type stuff with plenty of harmony singing). There are test recordings of percussion that do sound good so I put this down to the weakness of the whole reproduction system - recording to playback.
I appreciate that in your room you can't go the whole way as I have done but you can do some things. It depends how much effort you want to put in to this.
Nearly all listening rooms have major issues with bass. You may not have noticed this because of your high frequency issues. If you can do something to smooth the bass the rest of the frequencies, particularly the mids, become more audible, and that's where the main part of the music is.
If you just want to deal with the highs and mids, good positioning is important, and attention should be paid to reflections - off footstools, coffee tables, equipment on the front wall, perhaps the floor and ceiling and certainly the side walls. You could experiment using absorbent materials like a duvet to find out if any of these are issues. There are decorative panels of a size that can absorb mids and highs. Some can be made to your designs/photos etc..
I use pretty much 'The Thirds' positioning as described here:
http://www.barrydiamentaudio.com/monitoring.htm
As has been mentioned you could also use DSP or EQ but I've no idea how you could do that with your set up. I see the Marantz can use a Parametric EQ (PEQ) with Roon. I have a headphone set up with a computer as source and on that I can use JRiver as music management and it has a PEQ and Graphic EQ (GEQ). My speaker system uses CDs and the EQ is from a Behringer DEQ2496.
If you want to do things properly the first thing you need to do is measure what you hear at your listening position (LP). You can do this with test tones and your ears, or better an SPL meter. The most accurate way though is with a microphone and software (the free Room EQ Wizard - REW - is often suggested and that's what I use). Once you can do that (and it takes a bit of learning) you can make adjustments - moving speakers, LP - and measure again to compare. To control bass if you can't use bass traps, you could employ one or more subwoofers, or just DSP or EQ.
I bet you wish you hadn't asked!