New Sound System in '98 Bonneville

I am going to install a new headunit and upgrade the speakers on my 98 SLE. Is it possible to keep the steering wheel controls?
I saw another thread on this about buying some sort of adapter but I find it hard to believe there isnt a way to just plug in a wire into the new in-dash player. If not, will keeping the stock cd player have an effect on the sound quality with new speakers?

Another thing, the front speakers look very small... do they really make 2 or 3 way speakers that size and if so... at that size are they even worth upgrading? (it doesn't seem like they would do much)

Any response would help, I would like to get this done soon.
Thanks