Hi there, I am having the
exact same issues with a Focusrite Saffire pro in Yosemite on my 9 series board, the sequence of working/ not working is very similar.
1st i installed a firewire card (Syba low profile one with Ti chipset) this is the exact card others are using here for pro audio without issues. I didn't install any kexts for this, the card is recognized by the OS and I have read that is all that is required (although maybe we are both wrong and some sort of kext is required by Yosemite!!??)
Next I installed Saffire mixcontrol, all good, no problems....
Upon connecting the Saffire it was detected by the Mixcontrol software which told me that a firmware update was required before I could do anything else, so I allowed the firmware update, this went fine and it told me a reboot was required....
After the reboot it worked for a few mins then I experienced the EXACT same freeze as you
When it freezes the audio goes into a short repeating loop and the system is unresponsive to any inputs.
Hard power off was required- due to this type of freeze there is no console info to help with trouble shooting
Then I half remembered something about cables (my brain is soooo full of half understood info ATM!!!!) so I tried a different cable (with FW 800-400 adapter) on a different port to the one I used for the firmware update and.... Perfect!!! it was working great for about 4 hours solid- I was so happy- I tested the inputs with various mics and tested the outputs- everything was working (although I hadn't tested the spdif or adat) that night I went to bed with a BIG smile on my face
The next day I turned it all on and got the "short repeating loop" freeze after about ten mins...I hard powered off, disconnected the Saffire, turned back on and all was good, no feezes- onboard audio working great in Logic Pro X. Tried again with the Saffire which was OK for about 1/2 hour... then- short repeating loop freeze. I tried both FW leads in the various ports on my FW card but the short repeating loop occurred again and again, sooner and sooner each time.
Now I am at the point when I can use Logic Pro X with the on board audio flawlessly, for long periods- no drop outs or buffer issues and importantly no freezes, but as soon as I connect the Saffire I get a near instant freeze- at times before I have even fired up Logic- just playing iTunes!!
First I thought this was related to the Mixcontrol Software conflicting with the AppleHDA kext from Multibeast, so I replaced this with the original AppleHDA kext but still got the freeze.
As part of my testing I have also connected my Alesis MultiMix 16 Firewire desk to my hack (although this has no Yosemite drivers) and experienced the same freeze after a few min's- so this could possibly be a firewire implementation thing on Yosemite (or 9 series mobo's with Haswell cpu's) but to be honest much more info will be required to draw a conclusion here....
I managed to save a log of Saffire Mixcontrol crashing just before one of the freezes, maybe this will shed some light on the situation. Maybe a resident expert can find the time to look it over
To be honest I am glad I have found someone else with this issue- we can't be the only ones who have built a Hackintosh recently for pro audio use and are having this FW issue- hopefully we can sort it out together !