Female XLR to RCA?

In most cases, this should be fine. Though, if by design the preamp only has balanced outs, it may expect a balanced power amp, so the output gain of the preamp may be 3db lower if you use an XLR to RCA cable or connector. The impedance may also change, but typically it should be fine. 

What preamp and amp are you matching together?

@blisshifi 

Juan, correct me if I’m wrong, but as long as the impedance of the amps input is at least ten times higher then that of the preamp it should work.  Right? 

You'll only get an advantage if your amp/preamp are differentially balanced.

@blisshifi an SPL Elector to a Musical Fidelity X-P200.

XLR is really for Pro use with long runs, prevents interference to signals.

One advantage of XLR in short runs in home systems is that it is a LOCKING connection, whereas RCA connectors can be problematic, even sporadically problematic. Lot of cables, mess with this cable, it disrupts that cable.