Crappy sound from VW stock HU -- suggestions?

[chuckdubdubdub]

I'd post this in the general audio group, but traffic seems so low, maybe it will get more views here.

I've noticed not so great quality from my non-monsoon HU from my VW Beetle.  Seems kind of harsh on the high end.  I'd replace it with a nice Pioneer HU that I have, but it seems that compatibility with the Phatbox is questionable.  Another idea is that I've come across a digital signal processing unit, like this: http://www.caraudiomag.com/testreports/0602cae_cleansweep_cl441dsp_car_equalizer/index.html
Crutchfield says is supposed to drastically improve stock sound.  The bottom line is I'd like to improve the sound but keep the Phatbox.

thanks for any suggestions,

Chuck