Looks like you have a kick ass machine there. If you want to maximize your core usage while converting from .avi to dvd I recommend you try FAVC
It's no longer being developed afaik but it works with Vista and Windows 7 and has a 64 bit version. You can update to the latest HCenc beta just by copying and renaming the HC enc exe file. The latest HC beta is available on the same site as the above link.
FAVC will analyze the input file and launch an encoder for each CPU core to encode a range of the input file, then it will process the audio and mux everything back together and author the titles. You can set it to burn with Imgburn or just output a VIDEO_TS folder or an .iso image file. It maxes out my cores at 100%.
Oh yeah, and it's free.