I spoke to a guy from car audio city yesterday, and he said that the cheapest and most effective sound system upgrade for my BA XT 2003 model was to buy a 5 channel amp, and a 10 inch sub woofer... with the amp providing 75 watts to the sub. This is keeping the original speakers and head unit. The quote was $600 for his cheapest of the two including installation.

I don't want to spend any more than this and replacing the speakers in the car would not make sense because I will be selling it in 3 years. At least with this option I can take them with me.

Thoughts and opinions would be appreciated. Has anyone tried this??

Well at first glance id say expensive, but then i have some questions.

a 5 channel amp? so i guessin u want to run all the stock speakers off this amp too?

75 watts to a *small* sub? not too sure if its going to have much kick for you

Advice?
I would recommend not amplifying the standard speakers (as you will proably just destroy them), and instead, going a nice Jaycar amp (CAT. NO. AA0420) (2 x 80rms ( 1 x 200rms @ 4ohm)) and getting a nice good 10" (around 200 in a box) and install it yerself for 200 cheaper.

Just a thought anyway...anyone else?

Yeah not a bad recommendation, there's probably not a great need to amp the speakers, when you're only looking at getting a little sub, for a bit more bass.
Get a Sub in a box, and an amp to run it mounted on the back, and it is totally removable anytime.
Unless you want a good single sub or multiples, the stock speakers will still keep up, they aren't all that bad in the BA's.
It'll save you some money too. Probably cost about $300-$400, for something reasonable.

Do you have premium sound? As in the 10" sub in the back already? Jump on www.fordxr6turbo.com and do a search on upgrading the stocko sub - apparently some blokes are just changing over the standard sub with good results.

I only just removed the stock amp and installed a monoblock amp in its place, as well as two boxed subs. Used a line convertor for the amp signals (tapped into the rear speakers) and ran new power wiring (remote wire off the ciggie lighter wiring) and it made a huge difference. I wouldnt bother with amping the front and rear speakers. You could probably do it yourself for around $300 - I already had the gear from a previous car.

Nah I just have the standard sound. I thought it was crappy speakers that made it distort beyond volume level 25, however I used a real cd in there last night and it sounded fine up to about 32. I might just invest in some cd's and throw my converted MP3 discs out, haha.
Cheers for your help.