Recommendations please for good, affordable pre-amp for system?

@oddiofyl , you really need to listen to some good integrated amps before you condemn them. There are very nice units out there these days from Ayre, BAT, Pass, Hegel, Allnic, not to mention my VAC Sigma 160i that put a hurting on many separates these days.
That even address' @labtec post about running with the same brand preamp/amp.
I sold over $20K worth of separates when I heard the VAC 160i.
Sure, that is probably not a good match with the OP's Thiels, but I bet the Pass, Ayre, Hegel or BAT would drive them just fine.
Oh, and one less power cord and pair of interconnects to buy. ;^)

Donzi, I think you heard me correctly. You are in a situation where you have the potential for a great system, however currently short of funds. 
Don’t panic, Buy a used preamp that can be sold when you upgrade.  After all you can’t tell what you have without a complete system and the ability to listen comes 1st.

Your amp has an input  impedance such that it would match with most preamps, tube or solid state. 50K unbal, 30K bal.

I mated a tube preamp with a solid state amp. I like what this does for a digital system. Not saying this is what you need to do.  I would search the AG marketplace, purchase a pre that will serve you short time and when in a position to upgrade you can sell without losing many $ considering your use.

Take a look at the AG market place.

I love the Thiels, although you're pairing speakers that could potentially be described as on the "lean and bright" side (at least that's how I recall hearing them), and an amp that definitely fits that description.  You might look to a preamp that could add some warmth, fullness, and flesh to the sound.  That's a tall order for under $500.

One such option is the Marsh P2000t (which I used to own many years ago).  Or you might consider a preamp from a company such as NAD or Parasound.  Or, if you're handy with a soldering iron, consider one of the Bottlehead (vacuum tube) preamp kits to put together.  

To be completely honest, though, I'm with jmcgrorgan2 in that I think you should sell the Bryston and use the proceeds plus that $500 to get a really good integrated that mates well with your speakers.  I truly think you'll be much happier in the long run at that price point.

Otherwise, if you can save another $500-1000, you'll be able to choose preamps in an entirely different league that will fill out your system much better.

Michael

Thanks all! I've gotten a great deal from this group, and am grateful. OK, for the either now or future route, if reasonable money weren't an object, are there any additional recommendations? Michael, I am SO intrigued by the tube preamp kits. Where would, say, the 300B rank with other manufactured gear? Believe it or not, I was thinking yesterday that surely the information is out there to grab a schematic and build my own. All the better, already in kit form. This is almost a surety to try this, although I risk a grand, without having the ability to audition in, and decide if I like it. Even so, it's less than some other options that I also wouldn't audition.

You had mentioned Parasound. What about Halo P3?

And if I do sell the Bryston, what would you recommend for Integrated? And if I go the tube route, is this still your recommendation? Thanks!

@donzi , the 300B is tube usually used in SET amplifiers. The only preamp that I can think of that uses the 300B is the Manley Neo-Classic 300B.

I agree with @sufentanil that the Bryston/Thiel combo would be too bright for my tastes. However, I do understand why they make so many different flavors. Different strokes for different folks. Some people love extreme definition.

I have a friend who loves his Thiel 3.6’s. He has found the best combination to be a tube preamp (CJ), Classe amp, and Kubala Sosna cables. All of his electronics and cables have a reputation for being warm sounding, which is why they probably mate so well with his Thiels.

As for integrated amps, I don’t know that a tube integrated amp will drive these speakers properly.
I think the Thiels crave SS power. A BAT integrated may give you the taste of tubes though, with a SS output stage (150 wpc). Pass Labs INT-150 is also very popular, though no tubes are used.

Also, how large your room is and how loud you like to listen will determine how much power you need. Will the 125 wpc of an Ayre AX-5 be enough? Or do you need the 250 wpc of a Hegel H360, or maybe even the 400 wpc of the CODA CSiB or Jeff Rowland Design Group Continuum S2? Only you can make that decision.

Happy hunting,
John