Theoretically, yes this is possible. But it wont sound great and isn’t the best solution to the issue..
A better solution would be to get a small mixer (EG Yamaha MG06 (3rd Gen)) and feed both controllers through that.. You gain better volume controls, better mic inputs and balanced outputs from the mixer. Win Win!
I would not recommend any of the Behringer mixers that you can get for a much lower price however – they will break and let you down at some point – wheras a Yamaha/Mackie/Allen and Heath mixer simply won’t die – or it will take much longer to die..
My Behringer mixer lasted a year of slightly more than weekly use before it dies.. My Yamaha is vastly superior sounding (and although it isn’t a year old yet) will last much longer.. 🙂
bob6397