Help -- my system is too bright

Now, this brings up another point. Already, some posters are counseling cable and power cord adjustments to give this system ___. This, IMO, is how people get
duped into blowing a lot of unneccessary money on cables.
Cables will not produce ___ in speakers that are not built to accomodate it.

This the Krell sound that I also experienced - hyperdetailed. I SHOULD have experimented with various cabling & tweaks before selling the amp for something different, but I *thought* that I knew better. I didn't listen though & now I wish that I had. Because that *next* amp, while not sounding hyperdetailed, exhibited some other issues, as did the next one & the one following that.
Possibly a different amp (but only possibly) yours may synergise better when everything else is tweaked in. I would approach the fine tuning issues by trying & applying some tweaks instead.
Here are some possible examples:
cones under your speakers
Speaker cables.
Interconnects.
Upgrade AC cords.
AC line conditioning.
Shelving.
Cones.
Footers & Pods.

Does "digital hash" or noisy AC cause high end brightness?

I hadn't noticed this question initially...
Yes it certainly does - the radiated noise emanating back out onto your AC line contaminates the AC power supplying other components. Line conditioning can significantly attenuate that phenomenon, as can a filtered AC cord. The JPS Digital (filtered) AC cord is one common cure for brightness issues. Custom Power Top Gun or BMI Eel are other filtered cords, & of course I'm only barely scratching the surface regarding these filtered cord offerings. But do try the line conditioner, which should also benefit in that regard.

perhaps an RC Zoebel network installed across each of the tweeter's terminals may help, if in fact the ringing phenomenon is occuring. Dunno exactly how that could be verified, but it may be a fairly easy experiment to try out a network. I've never done one so can't explain how the RC values should be correctly calculated - member Sean may be able to assist with that; he's done this before.
Speaker cable HF rolloff can be related to cable capacitance / inductance; higher values of distributed capacitance in parallel with your load (the speaker) would somewhat attenuate the HF response, as would higher values of series inductance. MIT speaker cables may be worth trying here; they're internally networked by design, & can help to smooth out a brightness problem (it worked for me).
Regarding the 2 prong CDP AC cord: here's some ideas. If you want to experiment with a 3 prong style cord, then temporarily use a short (4" to 6" long) external handmade adapter device to convert from 2 to 3 prong IEC. During the experiment, the AC cord's shield will only go as far as the adapter, but if you like the sonic results then the IEC on the CDP can be changed to a 3 prong style, leaving the 3rd ground conductor unterminated if desired, or perhaps tied to chassis if no undesirable effects are introduced by doing so. Or the IEC on the end of the cord could be changed to fit the CDP's socket. Or the adapter harness could remain permanently if it's very short length & is made from quality conductor materials. Lots of options here. A Highwire Powerwrap helical adjustable filter installed onto the AC cord may be anoher inexpensive option to try.