MI4 Hardware and Audio Out Query

I recently resurrected my MI4 media interface that had been gathering dust on a shelf. I have a 2012 MacBook Pro running OSX 10.9.5. I want to use it for both MIDI and Audio purposes: digital piano MIDI out to Cubase Elements 7 and guitar input, out to Pod Farm 2 which is an insert within Elements as well. So here’s how far I’ve got:

I have two nEar 05 monitors that are currently being fed the audio output from the 3.5mm headphone jack on the MBP

MIDI works without a hitch. Signal from the digital piano via the MI4 and into Cubase just as it should. Output is heard from the monitors as you’d expect as well.

Audio is where I have the issues. To begin with I removed the 3.5mm cable and put 6.35mm guitar-type cables in the output L and R sockets on the MI4 and plugged in to the back of the monitors. Plugging the guitar in to the Instrument In socket and tweaking the MI4 control panel lets me hear the clean guitar signal for monitoring purposes but this does not go via the MBP at all. What I did notice even here though was a lot of regular ‘popping’ and ‘clicking’ through the monitors that I didn’t get when using them with the built-in audio.

Back in the main audio settings I set the sound output to MI4 and the told Cubase to use the MI4 for its output as well but nothing comes out. When I check in the audio/midi setup utility in the applications folder it shows the MI4 but when I click on configure speakers nothing comes out either.

Does anyone have any suggestions to get this to work or should I admit defeat (it is out of support after all) and look to replace with something newer?

Thanks in advance