You need to know how the XLR is wired. You need the service manual for the XLR equipment so that you know if the (I assume input) is balanced or not and if not, what pin is hot. Note that RCA female cable ends are not recommended because twisting the plug breaks the center conductor. It's a better idea to use a longer XLR to male RCA directly to the RCA jacks on the other equipment. Or use female "gender-benders". I would buy an RCA cable and replace the female end(s) with an XLR. If you don't already, you need to learn how to solder.