Found this on Xtant's site. Their website was down for short time but, is now back up and here's what I found in the faq:
"How do I use the RCA Outputs of one Xtant Amplifier to Supply Input to another Xtant Amplifier?"
Balanced Line: When using the balanced line on the first Xtant amplifier, all other amps receiving input from the first should have the balanced line Disabled, as they are already receiving balanced signal through the inputs.
Input Sensitivity /Input Gain (X series models only):
Remember, when supplying signal from one Xtant amplifier to another, the output of the first amplifier is already increased or cut depending on the position of the input sensitivity jumper. For example, if the first amplifier's sensitivity jumper is in the +10 position, the second amplifier will automatically be increased by +10 at the input. Therefore, in order to level match or gain match all amplifiers, set the desired input sensitivity in the first Xtant amplifier and then place all subsequent amplifiers jumpers in the "0" position.