Adding the SUT that is most attractive to one's unique preference is more the discovery to be made than the adding the right SUT.
Matching the SUT to the Cart' is only one sector to be a consideration.
SUT's add a Coloration to a presentation, it is a case of how 'Rich in Tone' is ones threshold able to entertain before it becomes a repellant and how much of a compromise to the overall performance is the presence of Richness to have.
Lovely Deep Rich Tones are easily able to suppress Upper Mid' and High Frequencies and completely paste over the details in a recording.
My preferred SUT's only add a hint of a Rich Tone and are not too far from the effects a Head Amp can have.
The Link has a Thread which is produced by an individual I trust, and have direct dialogue with via email on the subject of SUT's quite a few years past.
Not too long ago, I learnt that this individual favours the Ikeda Ist-201 as their 'go to' SUT, (this may have changed in recent times).
The Ikeda is able to be acquired for a similar price as the Luna, the Ikeda is also seen as a used item occasionally, so a few ££££'s can be saved.
SUT's are a voyage of discovery, I wish you a safe journey.