yrogins,
Just to let you know, I also use class D monoblock amps in my system, D-Sonic M3-600-M. They're also very neutral and revealing like your Bel Cantos are.
Initially, I paired them with a VTL 2.5 preamp with NOS (new old stock) Mullard tubes. This gave me a warmer, more immediate and dimensional total system sound that seemed very life-like; as if the musicians were in my room or I was at the venue, especially on good acoustic recordings. I think this is very similar to what you described as "intimate".
I think irish_tim's suggestion of a Conrad Johnson Classic SE preamp may also be to your liking. You should be aware, however, that both the VTL and Conrad Johnson only have unbalanced RCA outputs while your amps have the choice of either RCA or XLR inputs. You stated you'd like to try a preamp that has XLR outputs, if not a fully balanced preamp.
Here's a link to a previous Audiogon discussion of fully balanced preamps that you might find useful:
https://forum.audiogon.com/discussions/best-balanced-tube-preamplifier
Tim