upgrade what

It's 2026 and we still have people looking to tame sound with cables. We should all be embarrassed by that, and honestly angry with the industry.

In any case, the problem is your placement, your room/acoustics, or your speakers. There is no component you can buy to 'fix' that. I'm sorry that someone led you down that path.

eenie meenie miney mo - room, source, amp, speakers. Taming high frequencies with cabling is a poor choices.

Agree that toeing should be tried first to reduce beaming of high frequencies. Next is make sure room is treated properly. After that replace source and/or speakers for a more forgiving presentation.

Good luck.

I would start with tube rolling those (JJs?) small signal tubes.

corelli in our over 25 yeas of experience most of these grumbles only require modifications, not throwing out the baby with the bath water. and the 848s are excellent loudspeakers

when we put out a pair of 60k loudspeakers with diamond drivers we had to swap numerous amplifiers till we found magic.

the op has a good set of loudspeakers and amplifier the denon cd player is a weak link 

and swapping loudspeakers doesn't necessarily fix the situation

we take a holistic approach looking at all parts of a setup and many times these small tweaks can take a system to the level the op desires.

Dave and  Troy

Audio intellect NJ

I agree with @corelli that its hard to know if your in the right rabbit hole for your issues,  truth is you won't know until you dive in and dig around a bit.

It pains me to say I also agree with @audiotroy, :( whom I often see as self promoting, but honestly they are not alone, it just feels icky when they do it for profit.  That said they have a lot of knowledge and it costs nothing to speak to them.

Your Denon player is mid-fi relative to your speakers and amp.  I have gone down the DAC rabbit hole a bit starting with a few $ 2K units upgrading them to $ 3K, replacing them with a $ 5K and now am in the way beyond with my DAC.  To my ears I had very much the issues you have, and improving my DAC I could easily pay step by step to diminish the brightness and improve clarity and musicality.

The DAC in your Denon is probably not bad but not equivalent to most stand alone DAC's in the $1-2 K range which is the very least your system deserves.  If you want real hi-fi $2K is about the starting point for a DAC unless you go used.  

The old saying Garbage in is Garbage out, your Denon may not be your only problem but it is part of your problem.  Start with the source, deal with the room later.