Option1 If your car has the factory 6x9's then install a hi-lo convertor off of those speaker wires and run them into a four channel amp. Lower the gain running to the stock speakers and use the remaining two channels to power the sub. Upgrade 6x9's if you have the cash and put a bit more gain into them. Option2 If your car doesn't have the catory 6x9's then install the hi-lo convertor off of the front speakers and run the RCA leads down to the 4 channel amp in the rear and power the front splits off of the amp and use the remaining two channels to power the sub. Upgrade splits if you have the cash and put a bit more gain into them. Option3 Install two hi-lo level convertors and run the RCA's down to a 5channel Amp and run the whole system off it. Upgrade the remaining speakers if you have the Cash, 6x9's first (if none the upgrade splits) then rear door speakers. Option4 GO FREAKING NUTS! (my favourite, clears a whole day out for me ) install hi-lo level convertors run the rca's down to a 4channel amp with a pre amp output. Come out of the pre-amp outputs in to another amplifier and power several subs off of that. If going this step I would strong advise upgrading all speakers and doing the job properly. Also, PM Phreddy you has created a great little device that is much better then Hi-Lo Convertors for the Blaupunkt head units.