What I am looking to do is to get more spatial cues, and I suppose detail, to have a better sense of the recording venue and bring me closer to that sense of a live performance.Yeah, that makes sense. My guess is the combo of your class-A amps with a tubed pre is providing a lot of tonal color and density at the expense of upper-end treble or "air" that helps preserve reverb trails and better discern the scale of the recording venue.
I had a Bryson BP6 for many years, and it is the most neutral sounding component I’ve heard -- truly like straight wire with gain. When I put it in my system the whole soundstage cleared up and expanded so I could clearly "see" the entire venue with no veils. Given what you’re looking for, I think its big brother, the BP26, would be a perfect fit for your system and give you exactly what you’re looking for. Plus, it will feed your wonderful amps the full signal with adding or subtracting anything and allow them to sing more clearly and completely with their own pure voice. There’s a nice one available here now at a good price, so if it doesn’t work you can likely sell it with little or no loss.
https://www.audiogon.com/listings/lis9d507-bryston-bp26-mps2-solid-state
There’s also a Pass SP10 that would obviously have synergy with your amps, but I’ve never heard one so couldn’t say how it might help. My guess is it’s pretty neutral with probably more meat on the bones but less air and sparkle up top versus the BP26 -- but that’s just a semi- educated guess based on both brand’s house sound. Best of luck.