Hi There!
I had a KX-88 back in 1988! An excellent keyboard with a strong piano touch. The only problem with going down the master controller way is that you dont get any extra sounds. What are trying do? Are you recording onto the computer, or are you doing live stage work. For my money I think the PSR range of Yamaha keyboards have a lot to offer. I have a PSR-630 in you my studio. It has just under 700 sounds, full General midi and XG support. Built in disk drive, and a touch responce keyboard. It's great for studio recording/multitracking and also excellent stage use as you can load you backing tracks on the fly with the disk drive. Everything is together. No external mixing of keyboard and backing/drum machines! If you sing you may want to spend the extra money and get the PSR-740 or 8000. Both of the these have a vocal harmonizer that adds extra parts to your singing. The 8000 also adds a CD quality sampler. It is not as powerful as the pro gear - but enough to get professional results!
Please reply with more detail on what you want out of your keyboard.
Brad.