Recommend relatively obscure high end tube preamps

Just wondering whether people can offer advice on high end preamps worth auditioning. I am looking for those who have experience with more esoteric and expensive equipment (MSRP >5000). I've owned Wavac (never should have sold it) and now own the Aesthetix Callisto Signature. I've owned BAT, CJ, ARC so I'm not looking for answers on things you can readily find.

One that comes to mind is the Brinkmann Marconi. Any opinions?

What else is out there?

~ William