So let me see if I understand what Ian and Andrew are trying to explain: the DSP box essentially reduces some small differences in loudness between nearby frequencies as reproduced by the speakers. I guess this would be most noticable if you were playing music that included something like scales, or hitting each key on a piano sequentially. Even then the biggest difference (without DSP) should be something close to 5 db in the 60-90 Hz range which would be corrected to something less than 3 db by using the DSP.

This is a very subtle difference indeed.