Regarding the missing mid bass you referred to.
I used to own Quad 63's with the full Crosby mod for many years.
I eventually went to Atma-Sphere amps because they gave the fullest sound (especially in the mid bass) with the quads, which I found lacking in other amps at the time both tube and solid state.
I don't own Quads any longer (actually I'd love to hear your system) but I have stuck with Atma-sphere over the years, even eventually becoming their NYC dealer (talk about devotion to a product). You are welcome to come listen to the Atma amps/pre here in our uptown loft, and are about to get a new 16 ohm speaker in specifically to mate well with OTL's.
I'd love to compare notes with you as we're both in NYC. I'm always looking for feedback trying to improve the system and room, and happy to do the same for other people's systems.