@mmcgill829 As Stated, I have experienced many SUT's, a large selection of these on the home system, that are with retail Values of Approx' £300 - £2K and maybe even more expensive if listened to in other systems.
These SUT's are designs no longer produced, through to available designs.
Additionally, I have experiences SUT's that are produced using Tranx's referred to above and others, that have been utilised as a DIY Build.
As a result of Phonostage Bake Off's attended, I have experienced many Phon's used with a In Built MC Stage and a MM Stage with a SUT.
From a large range of experiences, I have not experienced too many SUT's I have thoroughly enjoyed and could live with.
Also when a SUT has been of real Interest, it is because it has produced something in the end sonic, that is much more wanted to be maintained than the MC Input can achieve.
As an individual with an all Valve System and a main Phon' being Valve Input / Valve Output design, along with Phon No 2 being a Valve Hybrid, I have selected SUT's that are in your description in the range of being Neutral. ( Richness being detected is a unique preference, it causes endless debate or blatant rejection, I've seen this regular in Group Assessments. One's own Get of the Bus point for a Tone is another's that is classed as best avoided).
The idea of having the Tranx's placed within the Phon' is an OK idea, but will be limiting to your experiencing SUT's or Head Amp's if they become a device of interest.
The Sculpture A has been referred to above, I have been demo'd these in both Copper and Silver Coil Tranx's and have been so impressed, these are on my must try in the home system short list, not much gets on to that list today.
A thread about SUT's and produced by a Forum member who's posts are looked forward to by myself is attached.