I'm planning to do a slight upgrade on my system. Currently running front stock splits, shelf Sony 6x9's both currently running off Sony H/U. I have a Kenwood amp and planning to run some splits and a sub off it and leave the 6x9's running off the H/U.

I'm interested in getting some splits from Jaycar. I was set on getting the 6.5" splits but I've just seen the 6" ones in their new Xmas catalogue. Not sure which ones I should go with, only about $10 difference between them.

I just purchased a Pioneer 12"sub 307 1200W and hoping to bridge it off the amp.

The amp I have is rated at;

Kenwood KAC-846
MAX power output 4ohms
100W x 2 + 300W x 1

Rated power 4ohms
50W x 2 + 150W x 1

Would this amp be enough to power what I plan to do or do I need a 2nd, more powerful, amp for the sub?

The amp should be enough. I would put all that in first and see if you like it. If you want more bass then you can purchase a bigger amp as another upgrade ( and possibly another sub ). Then you could use the amp to run all you speakers so either way it will not be a waste.

If you are looking at those 2 Jaycar, I would get the more expensive 6.5inch components.

Did you get the Pioneer in a box or are you yet to box it?

I bought the sub on it's own. My next question is do I have it installed behind one side of the back seats or would it be better to have it in it's own enclosure?

the sub put it in a box .......... unless it s a free air type i most doubt it tho

Yeah you will have to mount it in a box dude.

Why I asked is the other way to get more Db out of a woofer is mounting it in a more efficient cabinet. For example, if you mounted in a Ported box over a sealed box, although the ported box will be about 20-50% bigger, you will gain an extra 2-5db over a sealed box off the same power.