Using Multiple Inputs with Garageband: Troubleshooting

I've been using GarageBand for many years with a M-AUDIO PROFIRE 610 (firewire connection) to great success, including using multitrack recording for vocals, guitar and bass at the same time through the many inputs of the profire audio interface.

I recently purchased a KORG NANOKEY2 which uses the built input (USB in).

I've been trying to use both inputs, Profire through firewire port and Nanokey through USB port, simultaneously for recording/playback with Garageband but havent had any luck (Including trying to create and aggregate input that selects both these inputs and combines them into the once selection in garageband preferences. Since I've tried the nanokey through my USB, which works fine on it's own, I havent been able to use the profire 610 AT ALL in Garageband, even when the nano key is not connected - This is where I require some advice. I have changed preferences back to profire audio input and built-in output (which i've always used), and cannot get any input signal in garageband. However, when I open up the profire software there is an input signal coming through.

In addition to this, I can no longer get consistent playback in garageband, it seems to stop briefly every couple of seconds.

Advice please