have a 4 channel amp. all have speakers connected to them already. 6/9's in rear, 4'' door speakers. could i wire it to the amp in the same slots as the 4'' speakers? or is that bad?
You need a crossover but then you can connect it to one of the channels. Or you could do the intelligent thing and take out the 6x9's and run tweets on one channel and mids on the other, setup your crossover using your 4ch settings.
Do your tweeters have a cap in them? They might have a built in crossover in there.
I'd just wire them in parallel to the door speakers personally as long as those tweeters have a filter cap on them or a crossover or something with them. If you feel like getting fancy later you always can.