Well complicated !

Unity ,Shiva and some others uses physic engine, i've tried the demos and all runs really fine.
If you need very specific collision, you'll have to do it yourself; but for most cases : FPS, Car , the physic engines
goes well even on AAA games published !

So i htink it's ot each people to call the good Physix function
and adapt them to their A8 project !

Or switch engine or library if anything goes well ?
I don't know !
But for me i'll try to use Physix on my 3DGS sandbox tests !