Why does it sound better at lower volumes?

Hi, I have a Krell, a Slim Devices Transporter, and Aerial 7B speakers with Zu spekaer and ICs. The thing is this combination sounds fantastic, among the best systems I've ever heard at lower even moderate volume levels. The Krell volume control is incremented from 0-150. Anything less than 50 sounds sounds fantastic across the frequency spectrum. But when I go higher on many pieces the highs take on on a harshness that is like an axe chopping broken glass.

Don't get me wrong - a number of pieces sound great - often classical and even some rock such as Fleetwood Mac sound great. I'm trying to figure out if many of the newer i.e., last 20 years, recordings with compression and boosted highs are the problem. Is my system just too good reproducing the dreck out of studios these days?

I've noticed in the car many of the same recordings sound ok with the background noise competing with the boosted highs. They boosted highs are still there but aren't as annoying due to the road noise and limitations of the car stereo.

I've just purchased a balanced cable - the Transporter has native XLR and it's often said Krell sounds noticeably better with XLR. It hasn't arrived yet.

Secondly, I'm thinking about a power conditioner. The guy at the Cable Co. said my system is just very detailed and probably needs power conditioning. Interestingly he wasn't pushing a cable at all.

I live in a new house but the power source isn't discrete. I can wire a discrete one but don't really want to go to the trouble. I have a discrete source in the crawlspace powering a single bulb down there and one outlet. I'm thinking about running an extension cable from that to my system just to try a discrete run to see if I should go further down that road.

Lastly I'm thinking about changing amps. Again is the Krell too good for my own good? :) I've heard a lot of amps from the big and small names and I like the Krell. It simply sounds fantastic... on probably 20% of my music. But I'm starting to think maybe I don't need that 20% like I need the other 80%. :) Maybe some coloration and rolling off of the highs is better at the end of the day.

I have a Sqeezebox as well and have A-B'ed it against my Rega Apollo. The Apollo was a little better but the SB did pretty well against it. I moved on up to the Transporter but haven't A-B'ed it against the Rega.

I've got to do something here, I guess other than listening at lower volumes. I may try a new integrated, say, a Plinius, MF, or go to tubes. Problem with tubes, my speakers aren't efficient so I'd need to eventually change speakers if I go that route. I have recently heard a Manley Stingray on Spendors and Quads and the sound did have that certain ineffable quality of warmth and a good sound. Also same with an SLI-80 and Theils. OTOH, I've heard my 7Bs sound fantastic on other systems such as Theta.

Any thoughts on this conundrum would appreciated. At 46 years old maybe it's just my ears acting their age.

regards, David