In my trailblazer (w/o bose), the front speakers were 4 ohm, the rears 8. I added a crossover in the fronts and stuck a mid-tweeter on either side in the dash. What ohm's is this at? Here's the real killer question - in the back, I want to replace the 8 ohm crappers with 8 ohm woofers crossed over to tweeter. However, I also want to split the signal before the crossover to another set of tailgate speakers. I know that if i just added the tailgate speakers (8ohms) plus the woofers (8 ohms), it'd be 4 ohms. But, if I throw in the crossover with the woofers and cross them to 6 ohm tweeters, what happens? What is the ohmage? Is it too low for the stinky factory unit to handle? Gimme your opinions! Thanks!
Have you actually verified that the fronts are 4 ohm and the rear are 8? For the rear, you might as well forget about running a second pair of full range speakers with the stock HU. As to your other question, if you add 6 ohm tweeters, the tweeters will play louder than the woofers, assuming they're actually 8 ohm woofers. This will cause the amp to run a big warmer, amlost as if it were running a single speaker with a highly untamed impedence curve. My guess is that this will not be too big of a problem for the amp but I've never looked in depth at any Bose recievers.
For the front, if you crossed the tweeter and woofer properly (no peak in system response at crossover point) and the tweeter is the same impedence as the woofer, the amp will not see this as being significantly different from when it was only powering a single full range speaker.