Same as Len says really.....
A 4ch amp can be bought off Ebay for not much. It really will make such a big difference to the speakers. Then buy some comp's for front and rear (dont have to be that expensive, £200 will cover the cost for front and rears) I would say for a total of £250 you can have your car sounding amazing without the use for subs! If ever installation is of any troubles then please let me know as I will do it for free........I am in the building trade but off work at present and am very bored so anything to keep me busy!