Hi Bill,
With the canon sensors, the bayer matrix is RGGB, so AstroArt needs an offset of 0,0 in the colour synthesis dialog (see first pic).
According to some threads I found on the QHY forum:
http://qhyccd.com/ccdbbs/index.php?topic=3282.0
http://qhyccd.com/ccdbbs/index.php?topic=3109.0
The Sony sensor in the 12 has a GBRG matrix, so a 0,1 offset (see second pic)
Hope this works for you.
Edit: Are you doing the synthesis before or after stacking?
I always have it selected in the 'Options' tab of the preprocessor dialog.
PS. I had no end of drama's with DSS and the 60Da's 18Mp RAW files.
I trialed PixInsight and that was very slow to align and stack(Quad core i7), and I was not able to do more than 4 or 5 lights before I got 'out of memory' messages (even with 16GB of Ram!).
Trialed AAv5 and it was super fast and I still haven't hit a limit on the number of frames I can stack(yet). Sold.
For the price, I'm pretty happy with it.