I'm adding a Behringer CX 2310 crossover to my signal flow so I can add up a powered sub to my set-up. (Yes, the sub has a crossover in it, but it only has unbalanced connections and created the hum you might expect from unbalanced connections. Long story short, I can't use the crossover in the sub, so I'm using an external hardware one to handle that duty.)
 
MY QUESTION: I need XLR cables (L/R) to come out of the crossover and into a pair of Rokit 6 powered monitors. I have a couple of extra mic cables that seem to fit the bill as far as connectors (XLR male to XLR female). Can I use those for signal coming from the crossover unit to the monitors, or is there some kind of mismatch impedance or something... or whatever. I'm no electrical engineer.
 
Would like to not have to buy more cables if I can use some I have. Thanks for any advice!
 

Here's a link to the best article that addresses your connection issue:
[http://www.rane.com/note110.html ]
 
The short answer is that XLR pins 2 and 1 are the signal and ground (respectively) for unbalanced RCA inputs to the subwoofer.  Impedance does not enter itself as an issue in this situation, but it's still possible that hum problems can arise depending on how the audio 'ground' reference winds up being equivalent between the PC, the crossover, and the subwoofer. 
 
Write more questions as they arise. 

Balanced lines to balanced lines should be no problem. XLR, TRS doesn't make a difference as long as they are balanced. 

GaryMedia
Here's a link to the best article that addresses your connection issue:
[http://www.rane.com/note110.html ]
 
The short answer is that XLR pins 2 and 1 are the signal and ground (respectively) for unbalanced RCA inputs to the subwoofer.  Impedance does not enter itself as an issue in this situation, but it's still possible that hum problems can arise depending on how the audio 'ground' reference winds up being equivalent between the PC, the crossover, and the subwoofer. 
 
Write more questions as they arise.

Thanks very much. There may be more. The article is amazingly instructive. I “think” I get it. :) cables are on their way. I will be going out on the crossover, balanced XLR, to the sub, unbalanced RCA “in”. Crossover to powered monitors are straight XLR. We’ll see how it goes. Thanks again.

ampfixer
Balanced lines to balanced lines should be no problem. XLR, TRS doesn't make a difference as long as they are balanced. 

Cool , thanks. Crossover to powered monitors will be balanced XLR. Crossover to sub will be balanced XLR out to unbalanced RCA in on sub, the only connection option there.