Hi. I don't know if I understand well the problem, but here is my input: (I own a DTXpress IV)
According to the manual (and my personal experience), inputs 2, 3, 4 and 8 are stereo, and you can use a Y-shaped cable to connect two different mono pads.
I'm currently using Hosa YPP117, but I think Hosa STP203 will do the job too.