adding amp and sub and cap need advice

[super7]

2001 E38 with DSP. I am adding a JL 500/1 amp, JL 10W6 in high output box and rockford fosgate 1 farad cap to add the bass that is missing in stcok DSP system. How do i tap in with out losing DSP? also what is recomended punching out ski hole or totally removing rear deck speakers to make trunk a large ported box? Audio guy says that removing speakers would be better but i think he is in it for the additional cost. Any insights would be great. i do plan on eventually changing out the wide stock nav to a A/V unit. I got quoted $160 out da door for just install forgot to mention about the ski bag hole price seem reasonable?

Thanks in advance Robert

[staiman]

I just had the ski pass cut out in my car. Very pleased. Still has stock look.