So what would you recommend for my next upgrade?

I would upgrade the speakers. The Thiels need more power/current to perform at there best. IMO the 1.5's don't justify spending more money on an amp/pre or even a larger Bryston intergrated. Since you like the Thiel sound think outside the box(lol)and consider a Martin Logan-ElectroMotion.

Upgrade everything BIG TIME!!

I am not sure what your budget is for making changes, but based on my experience I would recommend you make fewer changes and take bigger steps, that is instead of spending on a bunch of tweaks, make significant component changes.

I would start with your analog front end given that you have 4,000 records.

My former turntable was a Rega P-25, which is a good record player. You have a Rega Planar 3 which is worth about $500 on the used market. I would sell it and buy a used Basis 2000 or 2001 with a Basis/Rega arm or if possible a Basis Vector arm. this will cost about $1,300 with the Rega arm or $2,400 with a Basis Vector arm. If you buy the Rega arm TT you can watch for a Basis Vector arm and upgrade later.

You could also upgrade your cartridge and phono pre first. Liberty, Lehman, and many others make a good phono pre in the $1,000 - $2000 range.

Cartridge is a matter of system matching and personal preference, so while suggestions are great you really need to hear it in your system to decide.

So overall I would take the front end of the system to an overall higher performance level, before tweaking the performance. Changing my TT and especially the tonearm made a very significant difference in my system.

Have fun finishing and fine tuning your system

Jperry - well "bigger steps" is an understatement. Hold on a minute while I catch my breath...:8) Not to be timid (I suddenly am) but TT + arm + cart + phono pre are probably well past my courage level not to mention my near term investment limit.

However, the cart + pre was, in fact, my thinking recently. But the challenge for me is how the heck do you do system matching with cartridges & preamps? There's very little in the way of shops up here in NH so component tryouts are really a challenge. Any reputable online places that will do business that way?

I would upgrade the speakers. The Thiels need more power/current to perform at there best. IMO the 1.5's don't justify spending more money on an amp/pre or even a larger Bryston intergrated. Since you like the Thiel sound think outside the box(lol)and consider a Martin Logan-ElectroMotion.

Not a bad idea...however, if he's content with the Thiels, I would suggest auditioning (not buying) a larger, more powerful amp.