speaker upgrade

I got a 97' tahoe 4 door and want to upgrade from the shot factory speakers. I was wondering if a person could convert the rear roof 4x10's to a couple 6x9's. Also any recommendations on a brand of speakers, I was thinking about some alpines or pioneers. I listen to music with a lot of bass and want a speaker that can handle the bass at freeway speeds. Most likely I'll end up putting some subs in later down the road, but for now I just want to upgrade the the door and roof speakers. Thanks for any input.

putting 6x9's up in the roof isnt too hard, the 4x10 is mounted on a metal plate 7x11 you can cut the plate to the size of 6x9 if you want, but you need to pay attention to the depth of the speaker, measure the stock one, it has a piece of foam on the back that rests against the roof, this is a good reference for the replacment, as for the brand, its a matter of preference, some people stick to one brand, ie pioneer deck pioneer speakers, but maybe look at a 6x9 with a movable tweet so you can angle it like the stock speaker towards the front of the vehicle