Best Options In A Balanced Preamp Under $1500.00?

I'm in the process of helping a friend who is a music aficionado, musician and budding audiophile build his first system. As a relatively young guy, his budget is somewhat limited. He will be using a pair of Monarchy SM-70 Pro monoblocks for amplification and now needs a balanced preamp, as those amps truly need a balanced signal for optimum sound performance.

If he had a bit more to spend, I could advise him, but in this particular range of price, I'm not as well versed. What would you recommend in a used balanced preamp as his best option(s)? I say used, because I am not aware of anything in that price range that can be had new, and also to maximize his investment. Any assistance would be greatly appreciated. Thanks in advance.