Who can convert single ended to balanced?

Wasn't there a company, I think it was JPS, that made a modification for the Thiel 3.5 EQ box called the Golden Flute? You might contact them--not sure if it's the same company as the one that makes cables now, but worth a try.

I think there might have been another company that made upgraded EQ boxes for Thiel 3.5s (the speaker that hooked me on high end, by the way), but I don't recall them, maybe others might chime in here. Is it possible Marchand might do something like this for you on a custom basis (I know that my crossovers are custom made by Marchand for my particular speaker builder, and they include a bass boost with a variable low frequency cutoff)?