Critique my system...

You shouldn't have any brightness problems with your amp and preamp. Although I wouldn't use the Monster cables, I don't recall where anyone's complained of brightness when using them, rather the opposite: overly warm and or/closed in.

The CDP you have is not in the same league as your rest of your system but again, it's not known to be on the bright side and their line of components are midrange centric anyway (which is not to say they limit the upper and lower frequencies).

Al is usually right in his diagnosis (if he had a 1-800 number and told people their futures he'd be a wealthy man by now) :-) so try his suggestions along with experimenting with speaker placement and maybe some room treatment.

All the best,
Nonoise

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.

As I reread your post I agree that the first step is to try some absorption room treatments. Acoustic wall panels, even furniture and rug placement can make a difference.
As far as your preamp, I doubt that an ARC would add brightness to your system.

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. :^)