You can use a different output on the waxwing for each system, or split or switch one output into both systems. I assume you want to use the digital outputs for both, but you could also just use the analog outputs into the headphone amp.
It looks like different models of micro iDSD have different digital inputs - some coax spdif and some micro toslink. If yours has coax then it's easy - toslink to the Apollo, coax to the iDSD. If it has toslink you need a switch or splitter, or a coax to toslink converter. See
this review for a couple of examples.