Critique my system...

All recordings sound different. Most CDs produced since mid 90's will tend to sound louder and brighter than most prior. WHat works well for older CDs might not for newer ones, making them sound bright and fatiguing in comparison.

Not possible to get all CDs to sound similarly good unfortunately. Recording quality and nature varies greatly regardless of format. Being abl to hear differences is a good thing.

Still, you want to be able to listen and enjoy most if not all recordings. Taming brightness/fatigue in general with most of the offending recordings is possible, but not with all.

So very important to assess what recordings sound good and which do not.

I have my system tuned so that 90% + of all my CDs are listenable and not fatiguing/bright. If you can get things tuned so that only a very small % sound fatiguing or bright, you are in pretty good shape. There are always some small % of recordings that will not sound good no matter what.

If what Al said doesn't resolve it, experiment with speaker placement and toe-in/out so that less sound reaches your ears directly from the tweeters and see if that helps.

Grills on or off the Boxers? That may make a difference if off currently.

Or try placing a piece of light felt or similar acoustically translucent material over the tweeters just for fun and see what that does. If it helps, leave it there. Tweak the amount of material used to obstruct the tweeter until you get the desired results with grilles on for best WAF.

All easy low/no cost things to try before changing anything. You'll probably learn more about how the gear performs along the way as well which can only help prior to making a change if it comes to that.

Brightness aside, how does the bass sound? Moving speakers around to different locations should have an effect there as well which might help with tonality overall. Those Nola's are rear ported, right? That would suggest they may do best overall including with the bass a couple feet or more out and away from front wall. Some distance from side walls as well to help avoid early reflections that smear the sound that might be heard otherwise is probably desirable as well.

Trying different ICs, not necessarily real expensive ones, might be the next thing I would fiddle with. A used pair of MIT Terminator 3 or 4 ICs for well under $100 might have a softening effect on the tonality overall.

Oh, and of course, whenever tubes are involved, make sure they are strong and functioning up to spec or else all bets are off.

If speakers cannot be well away from walls, then absorption panels or equivalent may help by reducing early reflections that help to smear sound, starting with primary reflection point from speaker to listening position for the speaker or speakers closest to the wall. High frequencies are most affected by absorbing panels so result should be less brightness in general, the question will be how much less which depends on many factors relating to speaker directionality and room acoustics.

Definitely worth getting a handle on how much of issue might be bass related. Panels won't do anything much to help with bass if that is what is lacking as opposed to too much treble.

Any tone controls on that gear? If so, use them. That's what they are for. :^)

I would not drop more than $100 max on any wire used just for the purpose of taming brightness. You'll probably find better deals on wires to experiment with on ebay than here.