Playing multiple hardware synths in real-time into Logic (via USB hub)?

I'm using a powered USB hub to enable me to connect multiple hardware synths to my iMac (e.g., Yamaha Montage, Korg Kronos, Access VirusTI, etc.). All of these synths are capable of supporting a digital audio stereo-pair + MIDI data over USB.

However, since audio preferences in Logic are global, and not track-specific, I can only select a single "input device" ( e.g., Montage), and only play and hear one external hardware synth at a time. I like to play multiple synths at the same time (e.g., holding a chord on one synth while playing a lead on another). Do I need to route all of my hardware synths to a single synth (pre-Logic), and only connect that single synth to Logic via USB to avoid constantly switching the input device assignment to a different synth? Or is there a way to hear all USB-connected hardware synths in Logic concurrently?