Brightness

It sounds like it might be a tonearm and or cartridge issue. Can you lower the tonearm, at the base to get a lower VTA? Try to get the tonearm level or slightly down in the rear when it is playing on the record. Also, is the stylus clean and in good condition.

Dave, it could be anything. If there is a single problem you need to locate it. If both vinyl and CDs are harsh then the issue is with your main electronics or speakers. Speakers would be the most likely. If CDs are OK but the turntable is harsh then you obviously have a problem with your table, cartridge or cartridge set up most likely or you could be overloading your phono amp. You have to go about this in a methodical manner.

Good luck,
Mike

More information is needed. 

What is the cartridge?

What is amplification?

What is the room like and how is equipment set up?

What is used for cabling?

What kind of music is being played?

The WT is a table with a plethora of adjustments, especially considering how much damping is applied by the cup. Who set the table up?

I believe its really important to know if the brightness is vinyl-only or vinyl and CDs. You need to figure this out first (as mijostyn stated).
Based upon my knowledge of the Zu Audio Souls M2, I don't think they are the cause, which is why I say check out how CDs sound. I have a hunch that it's your GCPH Phono Stage (I use to own one), but more information is really needed.

All the Zu Audio speakers have a rising treble above 10khz. Some call this "detail"!!! Same problem with B&W speakers.

+1 on GCPH , I have one I use as door stop.

Hang on a moment; what about a combination of factors, several links in the chain? As others say, first comes the vinyl/CD test.  But then... what if pre, power and speakers all were adding a little something to the mix, and the three together.....?  Bottom line, it may not be so easy to pinpoint, though inserting a mellifluous preamp should help.

Audiophiles routinely underestimate the effects of room acoustics on tonal balance. A better treated room can improve this, as well as make the system easier to listen to.

If you haven’t looked into room acoustics yet, I encourage you to. Good treatment will outlive everything else in your system. :)

Good way to tell is to set up the speakers so you are 2' in front of them and listen.  This will reduce room effects and give you an idea of your system's sound independent of the room. If you find that much nicer, treat your room.

Best,

E

Not everyone can afford it and those who live in a Condo,as I do, have very little choice in placement .

All the Zu Audio speakers have a rising treble above 10khz. Some call this "detail"!!! Same problem with B&W speakers.

Zu Audio speakers are not the same, supertweeter is different, depends on the model, high pass network can be upgraded with different caps.

I have no problem with my Zu Audio Druid, my supertweeter is Radian 850 and there is my previous supertweeter on the same image. The hights are silky and very enjoyable. 

Zu Soul mkII is way different from Druid
There is a huge difference in price between those two models, also huge difference in performance, so ZU speakers are different.

It is unclear whether you have the same brightness with CDs and with LPs. Let's start there.  Next, has this always been bright? Or, has something changed recently?  If so, what component change did you make that might correlate to the brightness?
You need to be logical.
Also, what recordings? Sadly, most modern rock recordings are bright.
So let's break this down logically and isolate what' what.  You can get good sound from lots of components. randomly swapping in megabuck products is just silly.

Dump the PS Audio IMO!

BIG 2nd to what Eric wrote about rooms. reflective surfaces can create horrors. Like i keep saying:
1. room2. setup3. source material
actual electronics are further down the list of priorities.
G

Dave, What is your preference to play? Vinyl? How is your TT set up? You mentioned you hadn’t played a CD for five years, so we can rule out play back from those. Do you stream? If so at what resolution and via who? Ethernet or Wi-Fi connection?
Dave, to help, a bit more information would be appreciated if possible.
AG Brissy

Try headphones to take the speakers and room out if equation.

EMF in my setup has caused unbearable brightness. I suggest, if you have not already, eliminating EMF as the problem source before blaming your system. What, if anything, did you move or reroute when your system became bright? Did you place any of your electronics closer than 3-5 inches? Do you have a power cord near or touching your speaker wires or any cables? Are your cables off the floor, especially power cables (rebar spacers @ 50 cents each are phenomenal for this)?

Cross your cables, if you must, at right angles, and don't let any cables touch. Keep power cords as far as possible from cables, at least 3 inches. I find that if I move cables in my system, for whatever reason, it takes at least 24 hours, if not a week, for my system to return to glory.

Recently I battled unbearable brightness upon substituting 4 expensive power cords for my stock PC's. Were the power cords incompatible with my electronics? I placed calls to manufactures and distributors, moved electronics around, rerouted cables, brought diffusers into the room, adjusted my speaker position and toe in. Somethings decreased the brightness, but nothing eliminated it. Ready to pull my hair out after months of searching for the source, I traced the problem to the 4 stock, unplugged power cords which, upon taking them out of my system, I placed in front of one of my electrostatic speakers. After taking the cords out of the room, the brightness vanished. 

The Unbearable Brightness of Listening

(Sorry....too obvious, couldn't resist.  Happy for you the demon was vanquished...*s*...)

All this negativity towards the GCPH......... I had one with the Underwood Mods and it is no way bright. What cartridge is he using and what load setting? Also, as mentioned above VTA problem?

The brightness you are talking about is probably because your system overemphasize the region 2 to 5 khz. Lots of us have the same problem with a great deal of available recordings. Try buy a Loki or invest in some digital processing to find out where your problem is. Fulle agree with eric above. Just bought an old pair of PMC OB1 speakers. 3-way with dome midrange to 3,5 khz. Very nice and detailed sund after some digital room treatment. Suddenly I can play the latest Van Morrison without hurting my ears too much from his (in this recording) extremely nasal voice (probably created in the mixing).

You could buy a better cable 
detail and more warmth Cardas a Clear reflection great combination try this on the interconnects ,also your fuses stock fuses are cheap gritty bright zinc fuses 
buy a quality fuse the synergistic research blue are still at 30 % off
vh Audio also has in slow blow only 
the Hifi tuning copper fuses I replaced all m6 fuses a a Huge improvement is much more natural sounding as well as detail ,seperation but need 150-200 to fully settle in  synergistic says up to300 hrs to full refinement ,also a nice heavy quality power cord will warm up the signal but at least $600 plus for a good qualityparts with copper gold connections like furutech 

I wish Dave (the OP) would answer the questions that were asked ;-)