Apogee Quartet CPU usage

Hi There,

I hope someone can help to resolve an issue I'm having when I use my Apogee Quartet. I have Logic's processing threads set to 8. When I have my Quartet plugged in to my MacBook Pro I get very high CPU usage - with virtually the entire project using only core / thread 8. It almost causes a system overload with only 4 tracks playing.

However, when I unplug the Quartet and play back the song plugging my headphones into the MBP my CPU usage is very low, with all 8 cores / threads sharing the load equally and I have no issues at all.

I'm using:

a late 2013 15 inch Retina MacBook Pro

2 GHz SSD Intel Core i7

8 GB 1600 MHz DDR3

Apogee Maestro 2.10.6

Quartet XMOS Firmware version: 1.2.12

FPGA Firmware version: a

QuartetDaemon version: 1.22.34

Recording to external Thunderbolt SSD

Logic X 10.2.0

I've also asked the same question to Apogee support but thought I'd also ask here in case they come back to me saying it's an issue with Logic / Apple rather than their stuff, and for the record I'm pretty sure it's an issue with their stuff.

I've attached two images of the CPU meter - with and without the Quartet plugged in so that you can see the issue I'm dealing with. I haven't changed any settings in the project between taking the two screenshots, save for unplugging the Quartet. The top image with the CPU spike is with the Quartet plugged in, the bottom image is with the Quartet unplugged. The difference is quite dramatic....

Would anyone happen to know why when using the Quartet pretty much the whole load goes through core /thread 8, whereas when I unplug the Quartet the load is spread equally across all 8 cores / threads?

Many Thanks,

Karim.

PS - I'm using the terms cores and threads interchangeably as I'm not sure which one I should be using....