I think the Storm dsp card that was later absorbed into/by Radius used the same dsp chips as are found in the 840av, and as the system software was multi-processor aware in the case of the AV Quadras, such a machine could simultaneously use all the dsp cards you can pop in.

As for software, Picture Press, a copy of which has been on eBay forever, used the Storm card for photo compression and for photoshop filter add-ons.

I have one of these Storm cards in a Q650, in which the acceleration is very noticeable. I suspect, however, that the card might be better suited to a 68030, where the speed would be even more impressive.