Seeking upgrade advice, specific situation...

If you haven't already seen it, there's a good writeup about the JBL soundsystem. You can find it by googling "Tom Morrow Prius JBL Audio" (sorry I can't yet post links due to being new on the forum).

Can you confirm If your Prius came with the JBL speaker upgrade? If so, there are 9 separate woofer and tweeters in the car (you can most easily tell by identifying a middle speaker on top on the center dash screen - if it's there you have the JBL system, if not, you have the standard stock speakers). If your Prius didn't come with the JBL speaker upgrade then there are only 6 speakers - separate tweeters and woofers in the front, and single full-ranges in the rear.

Aftermarket head units aren't really compatible with the JBL speakers, as the JBL speakers have separated woofer and tweeter connections that normally use a digital crossover in the amplifier to send the highs to the tweeters and lows and mid-range to the woofers.

 

If I had the JBL speakers and installed an aftermarket head-unit, I would replace the front woofers and tweeters with a component set wired directly to the headunit (not the JBL amplifier which heavily colors the audio). I would replace the rear speakers as well (again wired directly to the head-unit. In the rear I would use cheaper full range speakers (I don't care about the audio in the rear as 99% of the time it's just me or one passenger, and the rears just provide a bit of "filler" when listening from the front). Then I would disconnect and remove the middle speaker, tweeters in the rear, and JBL amp. After that, the next upgrade would be to add a subwoofer. Good luck on your system!

 

the problem with all this rewiring is that you'd have to just about gut the car to do it, and spend $1000+ to make it worth the effort. if you don't have the jbl its easy peasy.

wiring the rear speakers to the front outputs is a pain because the front tweeters are wired separate from the front woofers, so the crossover is in the jbl amp. but the rears aren't separate. I'd like to ditch the jbl myself, but I'm not gutting my car over it.

and, is there anything in the jbl system that needs to be hooked up for the nav, reverse cam, etc. to function properly?

 

unfortunately, the amp and head unit work as a pair; if you replace the amp, you must replace the head unit and re-wire it all. upgrading the speakers might not work too well either because the JBL amp is designed to use 2 and 3 ohm speakers. you can find 2 ohm woofers, but 3 ohm? what fu©ʞ!ŋƓ idiot thought that was a good idea? I hope he gets hit by a bus before he has a chance to breed.

 

I honestly don't think it would be too bad. I would connect into the existing speaker wires underneath the passenger seat. I'd run 4 pairs of wires from underneath the passenger seat to the right cable "tray" underneath the plastic piece under the bottom of the passenger front door. Then run these wires up to the dash and across to the head unit. If you've taken apart the dash to install an aftermarket head unit, then this shouldn't be too difficult (not more difficult than say adding a subwoofer in the trunk and wiring to it).

Those 4 pairs would connect to the wires that are already wired to the front, rear, left and right woofers. Then you just pop in aftermarket speakers where the woofers were. Of if you'd like, install a component system in the front, using the passive crossover connected into the wires to the woofer wired previously (you would have to run an additional wire for the tweeter, but this would be in the door and wouldn't be too difficult).

In this way you could re-use most of the existing wires, and wouldn't need to do any fancy wiring into the doors.

Also, the reason that that 2 ohm speakers were used is to get more power from the amplifier without having to build an additional power supply into the amplifier. From 13.8 volts you can only get 20-25W rms delivered into 4 ohms after amplifier voltage losses. However if you make the speakers 2 ohms, you can drive 45-50W rms. To get above this amount of power delivered, an additional power supply stepping up the voltage to 24V and beyond is used on aftermarket power supplies. Sucks for aftermarket installs, I know (but I understand the reasoning as an electrical engineer).

See this thread if needed. Some guys did like I was suggesting:

JBL Amplifier | PriusChat

 

when I upgraded the speakers in my '04, I went to parts express. the drivers they sell aren't name brands that you'd see in a store or catalog, but companies like visaton and Dayton audio make drivers for name brand home audio manufacturers. the woofers I chose were the largest ones that would fit that I could find, and they sounded great. my brother is an audiophile, and he made his own home speakers using parts express drivers. they sounded as good as high end speakers.
I did use alpine tweeters in my front doors because they clip right in with no mods to the triangle, and they sounded excellent. very crisp and clear but not harsh. I like to hear the tick of a drum stick on a cymbal, not the typical slushy sound you hear from most car speakers.