I misread what you posted, sorry. If you are just replacing the HU, no. You don't have to bypass the amp. If you are replacing the SPEAKERS, you don't have to. If you use 2 ohm speakers, you are good to go. If you use 4 ohm speakers, you will lose some volume. This weekend, I'm replacing the speakers in my 03 'rango with Polk DXi 650s ( it's my GF truck ) and if I get enough in my paycheck, I'm picking up two of the Alpine KTP-445U amplifiers. The truck already has a Kenwood KDC-945U HU, a Kicker 10ZX400.1 sub amp, and a Polk DXi 104DVC sub in a ported box ( got a great deal on all that gear ) Unfortunately, she blew out the rf speaker.And if I want to install a new head unit i have to rewire and bypass the amp??? Thanks!
I debated just swapping the fronts, and leaving the amp in place, then swapping out all 4 and leaving the stock amp, but decided I'll either swap all 4 and bypass the stock amp, or swap all 4 and put in the two Alpine mini amps bridged. I'll start a thread when I get home and get some work done to the 'rango...