aftermarket headunit hooked up...no sound

[BoostedA4203]

ok so ive been searching everywhere for info and have finally decided to go ahead and take the plunge..i have a pioneer avic f90bt and was under the impression that i could use the stock amp because i dont have DSP...basically all i did to try and see if things would work was disconnect the wiring harness from the radio module in the trunk and then connected it to the avic via wiring harness adapter...the radio fired right up but didnt get any sound...so what im wondering is will my only solution to be to bypass the factory amp by tapping into the speaker wires on the harness that leads to the amp? I really wanted to avoid doing this...any help would be great!