I tried the 6H23-EB's that ASTI sells for $45 (matched pair) in both the line and phono stages of my Mod3A. They are quiet, and long lasting--just as others have noted. They turned out to be too bright for use in both line and phono sections in my system, though. I kept the 6H23's in the phono section (because that seems to be harder on tubes) and went to NOS Amperex E88CC's in the line stage.
I agree with the other poster on this thread who mentioned that the Amperexes tend to be a bit forward.
The Amperexes' smoothness, transparency, detail, and front-ish perspective in the line section combine well with the 6H23s' dynamics and mid-hall perspective (also said elsewhere) in the phono section.
What other folks have said about the 6H23 in the Mod3A is pretty much my experience--other than I find them to be too bright for the double section dosage. I noticed the the VTS tube list mentioned this in the notes for the 6H23's vis-a-vis the Mod3A.