upgrades where to start, where to end

First time poster, but have lurked for awhile....

I'm decently happy with my system, but have done many things wrong.... example: I'm using a handme-down amp (no clue what the brand is off the top of my head. but it puts out 220w @ 4ohm. and has a built in cross over) through a Kenwood KFC-W3011 12" sub in a non-ported Phoenix Gold sub box

So I know I gotta upgrade the amp.

My speaker system itself is bugging me too...

So lets go through all the componets of my system:

• 2007 Ford Focus ST
• Kenwood DNX5120 head unit
• Kenwood KFC-W3011 12" Sub
• Phoenix Gold Octane-R 5x7's (front doors)
• Stock 'Sony Audiophile' 5X7's (rear doors)
• Phoenix Gold 12" Sub box (non-ported)
• some amp... 220w @ 4ohm

A list of things I want to upgrade (in order)

• battery (winters coming. and last season I had major issues with cold starts)
• Front speakers (move the Octanes to the rear)
• 6 disc Changer with FM transmitter (I miss my 6disc changer I had with my 2007 Kenwood unit. thats no longer compatible with 08 units)
• Sub Amp/box

I have no clue what to look for in upgrading the battery. Thats all new to me.

For Front' Speakers I'm thinking of going component system. But I don't know if I wanna start cutting around in the panneling of my car. Currently I love the high end response of the Octane-R's but they have very crummy mid-range. And my ear seems to be very sensitive to high-mids. Which seem a lil sharp. The rear speakers I find muddy and usually have the headunits crossover set to 100hz for the rears. The fronts have a cross over of 80hz.  But I blend most of it front anyways. I've been told to check out Clarions SRQ5730C for a straight 5x7 replacement, or I got a brutal deal on a set of Alpine Spx-177r. However the Alpine's are 6.5's and will require some cutting of metal and tweater install... (I want the tweaters at ear level for SQ)

For a Sub Amp I'm looking at either a Kenwood Excelleon or an Alpine Monoblock.

To be honest I'm very open to suggestions as I have very little experience in car audio components. I honestly just bought the components I have now because some sales guy told me too, or because I thought the components looked 'cool.' (ie the Octane-R's.)

Sound quality is overall what I'm looking for.

What I'm not happy with is the lack of clarity of the mid-highs and how lose the low end can be. I'm not looking to shatter buildings, but I would like clear, consistent sound.

Right now my budget is about $200 a month.

I listen to a lot of different music. Probably the most popular genere in my car is hard rock. But I listen to everything from Matthew Good, Jimmy Eat World, Nine Inch Nails, Tool, Chemical Brothers, Brian Setzer, Jason Mraz, NOFX... so something versatile.

The thing about the sub-amp is that I've been told by so many people that I'm underpowering it and I could blow the sub at any minute. 400w handling @4ohm, 1200w RMS is the number I'm pulling from memory right now.

Oh boy, now you've opened a can of worms...I spent an hour reading through this thread and all the discussions linked from it.  Enjoy! 

actually the 5120 does. it has three sets of outs. Fronts, Rears, and Sub. Even when you check the audio/crossover settings you can modifiy the sub. There is also volume control for the sub as well in a seperate menu.