Both of those files rendered OK in T2 it looks like.
Yes, I'm very happy with my work on the object import and thank you for the examples that helped me find and correct some bugs.
Splines and Rotated E-Arcs are fun (or as fun as math ever gets), but appear to be working great now. I'm still not sure how to deal with curves that only have one control point, they aren't Bézier so have to be rendered as cardinal splines but the DXF doesn't appear to include any tension value. I've noticed that Inkscape doesn't import them correctly either.
The negative space isn't a problem for T2Laser, with DXF's if the entire shape is negative it is ignored otherwise anything outside of 0,0 is truncated. PLT files are shifted to 0,0 if any objects are in negative space otherwise they are treated the same as DXF.