Audio Dropouts or insane CPU load

I have a MR 816 csx that worked like a charm on my windows computer,
recently bought a new iMac (3,4 Ghz i7 cpu, 32 GB ram, 10.8.4 OS X) just to experience the worst audio dropouts ever. If I was working on semilarge projects in Ableton Live 9 I could (when I was lucky) listen to a couple of seconds of the song before the sound dissapeared for 10-15 secs, when it came back it was more often than not crackling and messed up.

After scouring through countless of forum threads and hours of googling, I figured out a weird workaround to the problem, but its far from ideal. If I turn down the buffer rate in my DAW to 61(!) Samples, I loose the dropout problem, but the tradeoff is having a CPU load at 80-90% at times for projects that should be at 20-30% with a buffer rate of 512 samples.

I thought it could be a problem with Ableton 9 on Mac so I borrowed an Universal Audio Apollo Quad interface from a friend of mine to see if that gave me the same issues, but the Apollo was working like a dream. 20% CPU load at a buffer rate of 512 Samples.

At the time of being I can atleast produce music with this bufferrate workaround, but after having put a lot of cash in to a brand new computer, it is a far from satisfactory solution to the problem.

I have a feeling that the Steinberg drivers for mac are just extremely crappy, but would love some help with this problem if anyone have any tips that havent allready been discussed in the other audio dropout threads on this forum.