I did not bypass my amp. My headunit outputs 17 watts per channel, which is fairly typical. I tested hooking my speakers directly to the headunit, and it just wasn't enough for me.
I have read many people run through the amp. I did not know this when I did my install, except maybe I read one thread on someone doing it, and since I could only afford one headunit, I decided to play it safe (knowing what I knew at the time) and bypassed it.
Today's sound system concepts... excuse me... (engage old man rant mode)
I completely appreciate the new features of today's headunits. My entire collection fits on a tiny thumbdrive and even though my HU (Kenwood) also has a CD player, I haven't had a reason to use it yet. iPod capable, and adjusting for inflation, cheaper than the HU's of the 70's (my younger days).
But... 17 watts per channel is really pretty soft. Old school HU's were 25watt minimum, and 35 was pretty typical. Well, today it doesn't matter so much because everybody is adding amps and subwoofers. So the HU makers now can get away with cheaper internal amps.
I use my explorer as a utility vehicle. One day it's hauling bags of sand, the next day it has groceries, then maybe grandkids. What do I have to do to get decent sound? In the 2-door there is no space to mount amps or subwoofers. I went to a sound shop and asked them and they said they would have to research it and see how other people solved the problem.
(Yes, I could mount an amp and subwoofer like the JBL system does... I figure I'm out $300+ to do that and I'm a cheap SOB so that isn't going to work.)
What would have worked nicely was a high power HU and 4 nice 3-way speakers. I now have a low power HU and 4 nice 3-way speakers.
The good news... is that when I put $30 Pyle 3-ways in the front doors, I got enough bass to be ok with the set-up.
(old man rant mode off)
Have a great day!