As you asked offline about the Backert Rhumba Extreme and ARC preamps I’ll share this review that compares the Rhumba vs. the ARC LS17SE, which was priced $2k less at the time but just as an indication of the different sound characteristics…
As I mentioned, the ARC REF5 SE is an incredible pre and at a different level entirely from the LS17SE, and as you can get one of these used for around $6k that would absolutely have to be in the conversation. Here’s one that may still be available…
https://www.audiogon.com/listings/lis9ba7e-audio-research-ref-5-se-silver-preamp-complete-tube
The newer Rhumba Extreme 1.4 goes for $8500 new so a pretty dear premium to a used REF5 SE, but if you can find a used Rhumba 1.3 Extreme and can deal with only one fully balanced input (versus 2 on the 1.4) you’re looking at a nice discount to a used REF5 SE. Personally this would be a tough decision and would likely come down to which sound profile most closely matches your personal preferences so read the reviews. The good news — there’s no way in hell you’d go wrong either way, so there’s that.