Xlr Cables

I was thinking about buying some xlr to rca cables for my preamp to my amp becuse my amp does not have xlr but my pre does would this be beneficial or would there be no benefit.

nothing to be gained as it would not be balanced

I agree, nothing to gain. Even using XLR cables with supplied XLR ins/outs isn't really doing anything unless the gear has true balanced circuitry. Many manufacturers just tap off the line out to offer more flexibility with other gear. Or, if you were cynical you might think it on the deceptive side.