Sorry for the delay. If I understand you correctly, you can just plug your XLR mixer out-to-stereo inputs into one amp and jump these (e.g., with short XLR cables) into the inputs of second amp using the link connectors. Speaker outputs are strictly for speakers; link outputs are strictly for other amp inputs.
Would this apply to active powered speakers? I am getting a hum noise only on my Link/Out's. I just hooked up my new XLS 2500 and I have a laptop out to a mixer then out to the amp powering two 18" subs connected low pass and I have two active powered speakers getting their line in from the amp's Link/Out's. When I turn on the active speakers with no audio I get a hum. When I connect directly bypassing the amp to the active speakers no hum.