There are a few different models of the XM37 - the XM37, XM37 Plus, XM37 Xtra. I think all have slightly different specs...
I think most of them have 2 RGB inputs - 1 is a D-sub and probably 5 BNC's for RGB input 2 (R,G,B,H,V). You should be able to just feed 15Khz RGB in no problem to the same input. (Note it probably does not support 25Khz - but check your manual)