Factory bose rewire or not

You can interface with the Bose as long as you hook up the remote.

However, I would be concerned about impedance issues if you go in high level. I have done it in the past and it can work but it's a crap shoot. Could burn out the headunits internal amplifier. Also could have noise issues and the problem of too much votlage going into the bose system. This will make it so the volume will only go low to a point so after the first notch of the volume control is as low as it gets.

Use an adj. 4 channel adaptor or bypass the bose. If you choose to bypass you should change out the speakers as well since the bose speakers are usually 2 ohm or less and that won't be good for the head unit either.