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

Personally I have never liked passive line stages,  so with that said I would recommend an active preamp......especially if you want to set up a home theater....for just a little more than your budget you can pick up a McCormack RLD1 which has a HT bypass and is one of the better used values out there.  There is a Parasound  Halo P3 on the bay for $600,  another good value.   You have a great amp and speakers, don't use a receiver's preouts ,  get a dedicated preamp.     

Thanks Oddiofyi, great counsel. I have seen that unit on the web, and have it in my consideration/watch list. :)  I will gratefully check out the McCormack, another name I've heard several times now, but haven't looked into. Thanks!

donzi, you are correct. I had the > turned the wrong way, should have been <$500.

There is virtually no active preamp on the site right now that would do justice for the amplifier and the speakers that you have.
There is a nice passive unit, a Sonic Euphoria PLC passive line stage for sale on Audio Asylum for $625, maybe $500 gets it. As far as fitting in with the quality of your amp and speakers, that’s probably about the best you can do.

I would still consider selling the Bryston and going the integrated amp route, or using a source with a built in volume control.

You'll regret selling that Bryston in favor of an integrated....  I have a DAC that can drive an amp and although it still sounds good, it can't drive my amp like my preamp can.  Be patient, maybe listen to a table radio a little longer and save a little more..... That amp and speakers were $$$ when new, they are worthy of a nice pre.   

Of the ones you noted, I would stick with the Bryston.

Many people like to overthink things and mix/match brands of preamps/amps.  Sometimes it works fine, but other times it's a disaster.  

It can be particularly risky with passives where I've heard plenty of combinations that SHOULD work on paper, but they don't.  Again, sometimes it works fine, but is it worth the risk???

Don't overthink things...You have an amp by Bryston that I assume you like and are keeping...why not just get the preamp from them which almost assuredly would be a good match?

The odds of you hitting a bigger home run with the mix/match route doesn't outweigh the risk of striking out, imo.

If you are looking to hit a home run or get a sizable upgrade, then I would suggest going with both ARC preamp/amps.  Otherwise, you should be just fine with Bryston in that price range.