Upgrading sound system

[Badaxe]

So here is the gist of what's happening and my plan to resolve it. The antenna/defroster modulator cooked itself and I've been told that it is the reason for only getting two decent FM signals. While teaching my 8y/o the basics of fade/balance/base/treble we found that the rear speakers barely work and the front ones can't handle much of the low frequencies.

While I'm very capable of applying band-aids, I also have a sickness that has a taste for surgery(a minor one in this case). So there is a Double-Din standing by, I just need to find some basic better than stock speakers, and thinking of doing a roof mount antenna. The car is just my commuter right now so that's why I'm looking to stay just better than stock and not dropping in the 1500watt amp and Focal speakers.

So now for needed advise, has anyone done an aftermarket antenna and what speakers would you recommend? Planning on front components.