I have no ear for sound... none. As a result the stock CDR220 with the DSP (which you have) is fine for me.
I would recommend getting ahold of Woodie (aka; itsnotanova)
http://986forum.com/forums/boxster-parts-sale-wanted/52469-parting-out-whole-lot-boxsters.html and have see if he can sell you the parts you need to get back to stock. Or, go to a stereo shop that knows what they are doing and get that unit working.
Good luck and keep us posted.