I just realized that the JKU has for its larger sized speakers 6.5". On the wranglerforums website, someone, I forget by now, suggested unplugging all four tweeters and installing four 77kick10's(6.5"). I did that, and I was more than happy. The 77kick10's are coaxial, so unplugging the tweeters made sense, would be to0 much highs. But now I realize that the stock larger speakers for the JLU are smaller than the JKU"s by 2", they are 4.5". This leads me to think that the radio is less powerful, just a guess, and that one would have to use an amp to power upgrading all the JLU's 4.5" speakers to 6.5" speakers. I would say that upgrading to four 6.5" coaxil speakers and having no other tweeters plugged in with an amp would be the equivalent. I can't believe they downgraded the stock size speakers in the JLU. Doing this, would you still have to bridge the rear speakers? Seems like four channels to me.That second video demonstrated every step really well (wish I had seen it before wiring my sub). In the end I didn't go through the firewall at all. Instead, I went from the same battery post as the guy in the video, and then went underneath. If you look behind the passenger wheel well, there is a boxed rail that runs back the Jeep. I routed the sub power through that rail- which passes right by the rear drain plug (at least in the two door, there is a rubber drain plug under the carpet right behind the front seat). I ran the power cable back to that plug, drilled a hole in the plug (like he did with the grommet at the firewall), ran the power cable through the plug then a short distance under the carpet to come out under the seat. Everything is still waterproof, because the hole in the rubber plug is slightly less diameter than the power cable. I like this route better because if you're putting the sub under the passenger seat, it just doesn't make sense to me to run the power cable the whole way across the back of the engine bay, through the firewall, and then back across the Jeep to the passenger side (plus, to be honest, I didn't know about that factory hole in the firewall until I watched the video you posted ). Anyway, the route I used is completely protected- there's no way the cable is ever getting pinched or snagged (unless I crush the boxed rail, in which case I'll have bigger issues).
It's a good question, and one I wondered about as well. From what I can tell, although there are 8 speakers, there are only four channels. The upper dash and knee panel speakers all feed off the two front channels and the four speakers in the sound bar all feed off the two rear channels. When I went to the 6.5" speakers in the sound bar, I connected both speaker feeds to each speaker. I'm told this is called "bridging," and it really seemed to make the 6.5" speakers sound full- this makes me suspect there is a crossover somewhere in the rear channel wiring that directs different frequencies to each speaker in the back, but I could be wrong. Since my 6.5" speakers have both a woofer and tweeter cone, it would make sense they would sound better when they receive the full frequency range. Either way, the head unit only produces four channels of sound.
The KTP amps all four channels, and allows you to set filters on them as well (so you can limit the signal going to the front speakers to mostly high frequencies, and put most of the bass in the back- even if you aren't installing a sub).