The Best Preamp is no Preamp?

this is a case where specifics drive the outcome, generalities are fun coffee table chatter, but are inconsequential

Bingo!  This is totally system and listener dependent.  First, and most important question — what preamp were you using before?  My guess, if you actually demo a good preamp your song will change.  I’ve found the preamp to be, other then speakers and my room, to be the most consequential component in my system.  Also, your amps are meh so that’s something else to look at.  Ignore the preamp at your peril. 

I’ve used a preamp section of my marantz receiver (higher end one than op’s) when my actual preamp was sent for repairs. It sounded pretty terrible, to a point a stopped listening to music on that system until the preamp came back from repairs

Like adult diapers, it depends.

Using a Lumin DAC is an exception, as Lumin uses Leedh volume control processing which more than some have found to be superior to their high-end preamps. My Lumin X1 direct into MasterSound PF100 monoblocks using Leedh sounds great! Your mileage, of course, may vary.