@Retouch @sicijk No, OS X Mavericks is not the issue in this case.
I have been troubleshooting this all day, and even went as far as to downgrade a Macbook we have here at the office to 10.9 - turns out it ran Overbridge and Heat as a soundcard without any issues. I managed to find a Core 2 Duo iMac to test with as well - worked fine.
This seems to be unrelated to your computer or operating system so far.
I would say: yes, please update your Heat - whether it works or not for you is extremely important information to us. It will not harm your Heat, and a downgrade is not necessary.
This has been a very busy day - we're all working very hard at solving this. (Although it looks like the majority of Heat owners are not having issues.)