there will be a improvement but not as much of an improvement if you add even a cheep amp to your order. The output on that headunit is probably only 15wrms
the speakers you have ordered are rated at 55wrms so there will be a big problem with midbass due to the lack of power
something like this would really get the best out of those componants
http://www.caraudiodirect.co.uk/product_info.php?products_id=4139
or even better
http://www.caraudiodirect.co.uk/product_info.php?products_id=4140
cancel the order for the second set of speakers you wont need them add the above amp to the order instead and that way you will open up the possibilities of amping a sub in the future
Give the CAD a ring and say appologise for the error they a great bunch of guys im sure they wont mind
and whilst your there change the fronts to these
http://www.caraudiodirect.co.uk/product_info.php?products_id=3855
trust me you wont regret it