When I purchased my Focus it had the tape player stereo, I have since installed an aftermarket head unit with the wiring adapters etc. My question is this, IF I wanted to install say a CD6000 or even a CD6006 head unit, Would the wiring in my car be sufficient? Or would these two stereo's use different connections to my original tape player model?

I swopped a 3000 tape player for a 6000 no problems at all. lack of rear speakers could be a let down. I've also fitted a CD changer unit with ourt mishap

Lack of rear speakers? My Focus has front and rear door speakers.