Kinematics for XYZAB mill

I see your point and there are millturn machines (hence the sim you mentioned) but to justify the term 'turn' you need a rotary axis that can position as well as rotate at high speeds. If it's just rotating while the mill bit is engaged in the material then I would call that milling. I don't expect the particular machine you need the kinematics for has the ability to run the B axis as a spindle, but I don't know.
Usually a 5/6 axis millturn machine has a horizontal A axis that also works as the lathe spindle and a tilting head as the B axis. This is also preferable since bar stock can be loaded in the spindle/A-axis and the milling head can also be used on work held in the tailstock axis (ie 6th axis). On a millturn machine non rotating lathe tools can also be used instead of a rotating millbit.
 


 

Now that you wield the full might of matrix multiplication you can build your own!

After finally getting tired of doing the math by hand and switching over to sage I managed to get the offsets implemented: 

Video: user-images.githubusercontent.com/460672...784-f69c9e05f146.mp4

Sim config (requires version 2.10):    

Thanks, I do hope to get it into the sim collection but it won't be for the 2.9 release. The kinematics component in this particular sim config requires 2.10 due to some changes that have been pushed a couple of weeks ago.

Thanks to dngarret this sim config has just been pushed to 2.9 as 'xyzab-tdr'