Ya, you can wire straight into the amps if you don't mind all that background hiss and added distortion. It's up to you, sound quality is after all in the ear of the listener.
To answer the original question, if the radio lights up but you get no sound, it is *possible* the amps are bad, but not likely. More likely the radio is not *exactly* wired right. Did you connect the "amp remote" lead up? This is necessary to turn on the factory amps. This is the most common mistake.
If the radio does not light up, then the fuse under the hood labeled "memory" is likely to blame. This fuse has nothing to do with the amps, but is for your constant radio power only and often times gets blown during installation.
As for bypassing the amps, you don't want to do that unless you are ready to replace speakers and add your own amps/subwoofer. The factory JBL door speakers are 4", and won't sound too good when trying to reproduce full range music. The factory amp's output is crossed over, and the speakers have built in crossovers as well. You will get no bass at all without the factory sub.
I recommend that if you plan to use the factory amps (assuming you get them to work) that you purchase a "factory amp adapter" and connect it behind the radio. You will get much cleaner sound and you will not risk damaging the inputs on the factory amp from incorrect input voltages. They do run about $40 but they are worth it (like I said *if* you get the factory amps to work).