I record on an M-Audio revolution card. I want to playback through an HRT-X USB streamer into my powered speakers (The HRT really sounds good; better, to my ear, than the M-Audio.) But I can't find a way to split the record and playback function hardware... or, with the HRT-X installed, it isn't seen by AA.
You'd have to take that up with Steinberg; ASIO only supports a single device at a time - this is not an Audition limitation at all. There is a way you could probably do what you want though, if you don't mind a little more latency, and that is to use the free ASIO4ALL driver. This would let you see more than one WDM driver (hence more than one device) at a time.