Okay so maybe time to get back on the rails here...
What exactly is the point here?
None of this is doing any service to my original question, and seems more to be a debate about who is 'right.' The theoretical gear needed (or not needed) to 'prove' or 'disprove' anything is a pointless discussion. Everyone has different gear, rooms, ears, preferences, and opinions. It's also completely irrelevant to my question.
I fully appreciate that there are varying experiences here with SUTs, with some finding some pleasing improvement to their experience, and others not. All are valid experiences.
From answers to my original questions, it seems like finding a SUT with 1:10 and 1:20 options might be best since it sounds like there's been success with both and either should work with various configurations on my phono pre-amp. Some good suggestions on specific models to consider so far, but if anyone else has any other suggestions that might fit the bill, happy to check them out as well. Thank you to all who have provided some guidance on proper matching.