Are there any $1500 tube preamps that that can compare with Tubes4hifi's SP14?

"I think I’m most interested in the imaging and the details on the highs. Theres a little muddiness in the midrange but that’s not bothersome."

Of all the components, your current preamp is the strongest piece with regards to the above qualities. Your amp is a bottleneck, and most likely your source is too. One mismatched component can wreck your systems imaging and details.

Of the 9 pin tubes the 12au7 is going to give you the lowest gain which when setup properly will be a gain of 17 to 20.  This is where looking up the tube data sheets come in handy.

http://www.mif.pg.gda.pl/homepages/frank/sheets/093/1/12AU7A.pdf

A gain of 1 will be a cathode follower or amtube buffer.  Tube like the 300b, 845, and 2a3 will have a gain around 4

Mudiness in a system with decent components can easily be caused by the room.  The book How To Get Better Sound is an excellent resource. Running test tones through the system (30, 50, 100, 200, 500, 1k, 2k, 5k, 10k, 15k at a minimum) will help you map the room.   A poorly designed tube preamp may de-emphasize the low frequencies, due to the undersized coupling cap, thereby reducing the the amount of excess bass in the room.  If you have already mapped the room and added diffusers and absorbers where necessary you can ignore this.

Sfall and Ajcrocker1 those thoughts raise a couple of questions then on how to think about this. My thinking was this.  The leap between the Mod Squad and the Audible Illusions in sound quality was monumental.  It changed the experience entirely. I love what I'm hearing.  I want to improve upon it and try to get a little better imaging and detailed highs.  I don't really think about anything as a problem to resolve so much as improve on what I have.  I assume it would be just get an even better tube preamp.  I thought that the preamp had such a huge influence  that it would be the piece to continue to build upon.  So, if I was to swap out the preamp I have or the amp that I have, I would think a 1500 preamp vs. a 1500 (I could go up to 2k on that because the Bryston I wouldn't keep) amp would get me the bigger reward in improved sound.  I don't even want to know how Tidal's sound with the node compares to cd or high def digital.  Tidal is too much fun and I don't want to have a knock in my head against it because it will drive me nuts!  I have to see about what improvements configuration can contribute here.  

Have you read the book How To Get Better Sound?

https://www.amazon.com/Get-Better-Sound-Jim-Smith/dp/0982080700

If you have standing waves in your room a tube preamp may have nullified some the affect with less bass.   The way a basic tube preamp works is:
Source select to volume control 
Some sort of resistor divider to cut down on the input signal if the gain is too much
A tube
An output coupling cap

The coupling cap in conjunction with the input impedance into your amplifier makes a high pass filter.
cuttof freq is 1/(6.28*resistance*capacitance)
If any of the caps are undersized you might get a -3dB point at 15 to 20 hertz.   This would mean less bass

Your room has the largest impact of any component in your system. A good system is a hotel room that has not been treated will sound bad not matter how much it cost.

My suggestion is to do what you can to make sure you understand why you are having the problem and the strengths and weaknesses of the component the new component in question.

I purchased diffuser plans on line and had a carpenter make them.  This help the mids to low highs.  Added bass traps in the corners and that brought my room to neutral.  When you talk in the listening room it sounds very different than any other room.  Less echo and clearer speech. 

"The leap between the Mod Squad and the Audible Illusions in sound quality was monumental.  It changed the experience entirely. I love what I'm hearing."

I thought you were using the AI.

"I thought that the preamp had such a huge influence  that it would be the piece to continue to build upon."

In my opinion, the preamp is the most important piece to get right, assuming you made no major mistakes with your other components. Every component contributes to imaging and spacial presentation, so when I was looking your system over, I picked the components that were most likely the weakest in this area.

" So, if I was to swap out the preamp I have or the amp that I have, I would think a 1500 preamp vs. a 1500 (I could go up to 2k on that because the Bryston I wouldn't keep) amp would get me the bigger reward in improved sound."

You're over simplifing the issue. The biggest 2 mistakes you can make are using cost as a measure of quality and going with tubes because you assume they're better. System matching is far more important than price or design. In my own system I use $2500 speakers and have a pair of $10,000 sitting in my closet collecting dust. Tubes guarantee nothing. My advice would to be listen to a component and judge it based on sound quality. If it happens to be tube, fine. But if a SS components sounds better, then that's the one you should buy.