Best Options For A Tubed Preamp - $2500 Or Less, Preferably Used To Maximize Value

OP,

The importance of matching fully balanced and single ended components depends on the specific components and on where your overall system is. Typically, especially with really high end components like Audio Research, the difference is minuscule to non-existent compared with the advantage of the component sound. I would unhesitatingly recommend the preamp connected to a non balanced amp. When your system is just about at the pinnacle of perfection annd your splitting hairs… it still might not make a difference. Importantly, Audio Research and Conrad Johnson ant the like are designed to be incredibly musical and sound great regardless of the connection you use. 
 

Plus 1 @ghdprentice 

Audio Research has a really warm sound. I saw an LS28 that sold for $3250 a couple of weeks ago.

All the best.

If you can think outside the box of mainstream audiophile tube preamps, you should check out space tech Labs. The designer will answer the phone and ask questions about your current equipment and your sound preferences, then will design around that information. 

Counterpoint SA-3000 or SA-5 (5.1).  Then you are done except for upgrading.

Best and newest  Conrad Johnson you can afford