The 68882 is not a DSP chip!
It is a FPU processor (Floating Point Unit). Look at your accelerator: there is a cristal in there? Grab an used (working, of course) 68882 with the same or higher clock (NEVER LESS).
A FPU may come handy for some (not so few) applications, but not for system's overall performance.
Oh, and ANY trapdoor card is "glued" or soldered in the main board. Try to pull it out again or look if the board are not locked in place by touching the floppy drive, for instance.
