Your postp needs to have the toolchange section present in it. You may need a bit different code following it, but it would look something like this...
The Centroid inch post that is in V11 (added to your list by way of Machine Configuration Management) has the needed code for arcs in it. What does your design have in it for arcs/circles? If you choose to node edit them, do you see many nodes close together or just a few with arc segments between them? If it's many nodes, then your output will be segments. If you offset an ellipse or a shape that has a bezier curve, you'll get many nodes instead of just the few that made up the original. So, check your design for those conditions.
Agreed, it's gonna cut exactly what you output to the PP. If your curve is 1000 tiny line segments that's what it'll cut. For "art" type designs I always use the "curve fit" tool before I output the design file to the PP. This cleans up all those 1000 nodes and outputs a smaller and cleaner file that can be arcs or curves. There are several options in the Curve Fit tool so read the manual on the settings and I think it'll improve your designs and cuts.
If you cant fix your drawing (its so annoying how offset jacks up vector geometry in aspire), play around with some of cnc 12s smoothing setting qnd you can get it to blast right through smoothly