Looking for the best audio DSP add-on box that I can insert between radio
and speaker.

I have a relatively old Am-Com DSP speaker that I use with the IC-735 and
it works reasonably well though it doesn't really have any versatility (no
way to adjust the filter characteristics or depth). In any case I need
something I can use with the SP-5 speaker that matches the FT-1000.

Any suggestions appreciated... thanks...