As I mentioned, your DX10 Controller enables you to switch between DX10 and DX9 modes, literally with a mouse click. Well, that’s almost true….
Don’t forget that the Fixer will make changes to your fsx.cfg, as well. Now if there’s one thing that makes me very twitchy, it’s when external apps make changes to my fsx.cfg file without my knowing exactly what’s going on. I have weeks of my life invested in that file. So as well as the real file called fsx.cfg that fsx will use, I also keep copies of the two current versions — those that are correct for DX9 and DX10 — and manually (well, in actual fact I have little batch files that do it for me) copy the correct one across to the actual fsx.cfg file, just to be absolutely sure. Whenever there is a change to my fsx.cfg, I also take great care to save it to the backup version of the appropriate mode.