Hey Geno,
Just getting caught up with this. I run my UFOs as balanced monoblocks, and yes, pretty much anyone who makes cables can make the the XLR -> 2x RCA splitters. I actually made a pair myself but they were pretty rough. I got a pair from:
http://signalcable.com/index.html, just send him an email explaining what you want. I think it was $99 for a 5 foot pair.
Also
https://www.ebay.com/itm/124295003300?ssPageName=STRK%3AMEBIDX%3AIT&var=42518590... does really good work in my experience.
The pro tip is to ask specifically for the + phase to be the red RCA, that way you know which speaker terminal is which. See below re: your subwoofer amp.
As Lin says, you don't want to get off-the-self cables, they don't do what you need. I wish Decware sold these cables, that would make it lot easier (and maybe sell more amps...). The way I think about this is you are using the L and R channel of a stereo amp for the + and - phase of a balanced mono signal.
What is your source? This only matters if your source is truly balanced, and not just a single ended signal on an XLR output. I think the balanced monoblocks are fantastic, and if you pursue this you're going to be very happy.
About your subwoofer amp, you just need to know the + terminal on the side of your red connector (pro tip above) is the same as the positive connection on your current speaker and other + terminal is the negative/return/black connection.
This can be kinda confusing, but soooo worth it. Let me know if you have any other questions.