Another basic newbie question.

I'm not an audiophile but recently more-or-less inherited an older high end system. There is a thread here about that story. 

This is a simple question regarding the Audio Research LS16 preamp. I have the user manual but it is short and assumes that the user is a seasoned audiophile. I think I've got the basics figured out. I understand the RCA inputs and outputs. I have high quality XLR cables for output to the amp. But there are two inputs I do not understand. They are labeled CD Bal and Aux Bal. I understand that 'bal' is for 'balance' but otherwise I do not know what these are for or what that means. Are there CD players with XLR-out ports?

Thanks for your assistance.