Just purchased and really liking this bird especially as it comes equipped with GTN750 integration.  Simple question here...I can't get the AP to follow the magenta line!!  Tracking in heading mode is ok but when I switch to NAV mode on the AP the PA32 seems to aimlessly turn in circles??  Yes I have GPS enabled on the GTN750 as the source for the HSI but for some reason it does not follow the magenta line? 

Ok I pre-programed a flight plan in the GTN750 and the PA32 followed the magenta line in NAV mode as expected. The problem I had earlier happened when I had inserted a Direct To waypoint and seemed like the AP could not capture the magenta path. Strange.

The GTN750 has a customized method for "direct to" - you'll notice if you set a DTO where the desired track is anywhere other than in front of you (or say 15 degrees either side), it draws the beginning of the magenta line away from the aircraft; at the point where it estimates you will establish the direct radial.   (instead of from the point of the aircraft when the DTO is executed).

So yes, you could well be right, although it will pass standard GPSS commands for Flight Plans to supported FS aircraft, they may struggle with it's "clever" DTOs.