If you are looking for a simple upgrade, you need to get some 5x7 inch replacement speakers(polk, infinity, kenwood, etc...)with tweeters in them. They will fit in the doors without drilling, cutting etc. . As far as the radio goes, it doesnt sound bad, just doesn't get very loud before it cuts all the bass and treble out. I replaced my radio because:
1) the bass and treble drop at higher volumes
2) I wanted to use the dvd player that I paid 400 bucks for!
3) I am hooking up my old system, and have to have the best sound quality!
There are solutions out there to keep the stock radio, and build a huge system on it. Look at Audio Control's website, they have a high quality line converter that takes your speaker outputs from the radio and converts to low level signals for amplifiers. Or, buy amps that have speaker level inputs, most companys have some decent ones(MTX, Infinity). Since nobody makes any cx-7 specific install kits yet, you will need to have a system custom installed if you want amps, subs, or a new deck. I'm fortunate that I have the skill and experience to do this myself, but obviously not everyone has that. It's just a question of how quality you want your sound to be, and how much you wanna pay for it. Good Luck