Thanks so much for your thoughtful replies. I experimented- again!- with adding a decent Velodyne sub I have laying around into the equation, to check what my reference LP's might sound like with reasonable bass levels back in the system. Yes, that helped, but it wasn't a solution, as it got boomy as soon as a contemporary bass heavy LP (Beck) was tested. So . . . it occurred to me that the issue I was hearing was like phase inversion with speaker cables. Which led me to wonder if, given Herron's rep, he hadn't design a simple solution to a problem like this into this unit. And indeed, there's a mains phase inversion switch on the rear panel!. Click, and voila- instruments advance, and bass reappears, tightly integrated, not bloated, like I'd expect given everything I know about my system. Just for kicks I'll leave the Velodyne in there cut off at 60hz to see if it annoys or enhances. The gain issue continues, but for my low-volume habits, that's not much of a problem.
It's a testament to the PF7AR that the legendary Herron isn't a complete revelation. I'm now pretty far up the curve of diminishing returns- the Herron's nowhere near 3X better. It's a match tone-wise, and to its credit its reveal of the stereo spread across the x-axis is steps beyond. On certain recordings- Leonard Cohen's The Guests for example- the difference is magical. Otherwise so far it's not far from an even exchange. I'm not going to re-engineer my life for the sake of perfection, but taking everything into account, the Herron's a net positive. If I want to lean forward and be analytical, it gets me there, if I want lean back and hear the music as a whole, super cool that it's already doing that. This is all pretty new- I'm sure more insights will arise . . .