Ubuntu 13.10 no HDMI audio (Haswell 4600HD)

I have a System76 Gazelle Pro (v9) laptop which has a Haswell Core i7-4800MQ cpu in it and no seperate graphics card.

When the laptop came it was preloaded with Ubuntu 13.04 which causes loads of video issues so I quickly installed the drivers from 01.org and everything worked perfectly.

After the upgrade to Ubuntu 13.10 there was no sound output anymore through the HDMI output. I tried a clean 13.10 installation which did not help. 

I then installed Windows 7 and there the sound worked perfectly through the HDMI output. 

Then I went back to a clean Ubuntu 13.04 installation with the 01.org drivers and it was all back in working order.

The thing is that there is no support for 13.10 from 01.org so I can't try these drivers on 13.10 to see if it helps.