I have a Yamaha KX49, the little brother of the KX8. Out of the box it is set up to work with Cubase, but if you select Sonar as the DAW on the KX8 it emulates Mackie controller logic. You'll need to tell Sonar it is a Mackie device in the controller configuration then, bingo, all the transport controls will now work. You'll need to assign the correct MIDI drivers as well, either KX1 or KX2, I can't remember which. Make sure KX3 is disabled - this driver is for Cubase only. You can further customize the Mackie config to assign the correct functions to the buttons too. From memory, the Yamaha manual was pretty good about telling you how to set up Mackie emulation.
I've never been able to get the rotary knobs working properly with ACT. I suspect it's an ACT problem as I've seen others here report similar problems with non-Yamaha controllers. In fact, only Roland controllers seem to work flawlessly with ACT.
Sorry if this is a bit vague - I'm miles away from my system at the moment but happy to follow up later if you get stuck.