Tascam US 16x08 interface: Can only use one audio program at a time...why?

[Music King]

I always use multiple audio programs at the same time with all my interfaces, (I have five). But with the Tascam US 16x08 interface I can only use one at a time. My notation programs will state: MIDI/AUDIO device not available if I have my DAW or any other audio program opened.
Is there a work around?