How many lines out are you looking for? All you need is a basic Audio Distribution Amplifier. A cheapie from Radio Shack (cringe) would do the job: http://www.radioshack.com/product/index.jsp?productId=2103065&cp=&kw=audio+distribut ion&parentPage=search
The XLR out of the DJ mixer and the RCA inputs are the same line signal, so you do not need any signal conversion, just an adapter to go from XLR to RCA, which is also available at Radio Shack (cringe) or a Guitar Center. http://www.hosatech.com/hosa/products/GXM-133.html
The mixer should have no problem driving a signal 100' down a mic cable then adapt it at the DA to RCA. If you want a stereo signal, you would need two XLR's from the mixer to the DA, then two RCA's (L&R) to the boats. To keep it simple, you could also shoot a mono signal to all so there is just one wire to deal with.
You could also go with a "Press Box": http://www.whirlwindusa.com/press.html
But those can get expensive, even to rent.