kindly suggest your budget..
IF your budget is around 6k, then bro its too less for an upgrade for all the 4 speakers as you mentioned. Get 2 front coaxials for 6k, If you get Focal it would be great or else Pioneer, Kenwood and any other brand would also do. For rear keep the 2 stock.
6k is not a decent enough budget for the 'upgrade' you are looking for so the above mentioned combination is the best currently available to you.