critique my setup -- weak link? best way to improve?

Seems most want to flaunt personal experiences rather than address the OP's question 

Other information that is not known, is how the TT is mounted?

Is the TT sharing the same structure as a seating the Speakers are seated on?

Speakers at 20"s Tall will usually be mounted on a Stand or Sub Plinth and Stand that is typically not much more than 24"s inches in height, but usually between 18" - 24" depending on the height that is ideal for the Tweeter. Usually the Tweeter is a little above ear level or on the same height level as the ear, when stands are being selected.

As a conjecture, is the Side Board 36"s ?

Are the Speakers Toed on the Longitudinal Plane if the Tweeter is too high, in conjunction with being Toed on the Lateral Plane? Getting this alignment correct will take a additional amount of tweaks, and Pads as footers on a Speaker are not offering the finesse of adjustments that may be required. A Sub Plinth under the Speakers will always being a improvement to how tidy a Cabinet Speaker End Sound is being perceived. In this case it can be suggested a Sub Plinth with Footers that offer a broad range of adjustment will be the best suited design. The Pads already in use will be useful for the Speaker on the Sub Plinth, but again I strongly suggest a suspension type footer for this role.

Getting the mounting method correct will be beneficial to any Speaker put in to service, the time spent will be future proofing.

The TT is much much more sensitive and getting the mounting structure correct for creating the environment the stylus function at it best will yield great rewards, again getting this correct for the environment the TT is set up in will be extremely beneficial if changes are made for a TT further down the road.

Both the above mounting methods are not going to cost much monies, there are DIY designs that are extremely effective, the main cost could be how it is appealing aesthetically. On a Cabinet, a method to keep costs down, I would suggest looking at Kiln Dried Sand Filled Plinths.       

Seems most want to flaunt personal experiences rather than address the OP's question

when is not the case? Not only that, people sometimes just post links to what they are selling. Still, if you post a focused question, you will get a lot of useful advice 

Advice on what’s next?

stringreen suggested “just enjoy.” That’s the right answer for this question almost every time. If you’re pretty interested in an upgrade that will add to the enjoyment with the greatest bang for the buck, that’s where the interesting part starts.

I’m sure that I’ve moved through equipment in the last decade, sometimes without fully hearing what an individual piece was ultimately capable of offering. If it were my system, I might try a different speaker cable, just to find out whether I can hear that fine of a difference.

Or I might try a different pair of speakers, as in that case I should definitely be able to hear a difference. This might also be true with a phono pre, but imo this would be easier to hear once the speakers were swapped out.

All interesting inputs, I sold hi end audio for any yrs, and here it is

START with the source, get the best...(to your ears) source, then you have a reference to go by.....think of it this way, in football you have offense, defense, special teams, coaches, OC, special teams coaches, etc, the list is endless, where to start to improve the team.......the  OFFENSIVE LINE.... I am from The Boston area, and you can have all the Tom Bradys you want, anemic O LIne...he is toast, weird analogy to be sure but it fits.......Source 1st....we had a demo of turntables with the same cart thru a Naim Nait and $300 speakers, the difference was quite clear and that was to people who knew nothing about hifi.....source 1st.