I'm looking to spend around 600-700 on stereo upgrades and am not sure where to add first. I've read a lot around on here and have seen all kinds of opinions and ideas, some of which I'll likely adopt along the way, but I'm looking for opinions on what will make me happiest right now.

I've have new Polk db651s as my cabin speakers and will be upgrading to a dual battery set-up regardless (though the recent thread on the Perko switch vs. an automatic switch kinda has my head spinning).

So, I'm wondering if I should put the money into an amp for the cabin and add a subwoofer first? I would be doing the install myself I have a buddy just looking for a reason to use his cabinet making skills if i want a custom enclosure. OR, should I add tower speakers with amp for those right now since I don't have any tower speakers at all?

I've resolved that I won't be able to afford all the top-of-line stuff I've seen others rave about, but have seen others here say they have spent less and been happy too. I welcome any thoughts and ideas and appreciate the overall friendliness on this board (don't seem to see that too often in the message board world!)