Sure you can use stomp boxs on a keyboard. The problem is that most stomp boxes only feature a mono input, whereas your keyboard is stereo. So you'd either have to convert your stereo to mono or put the effects on only one channel. If you wish to use effects like this, it would be best for you to run your signals into a mixing board, and use an effects send to feed the stomp boxes (I personally run my keyboards into a mixer, and send them out on an aux send into a lowpass crossover, which feeds a Digitech BP-8 bass preamp/processor, which feeds into seperate bass amplification, in addition to the main stereo outs that sends full-range signals to the main P.A., and my personal Monitors).
I would personally recommend you check into some of the available rackmount units as well. These will usually give you more keyboard friendly effects, and most feature MIDI IN, for external control (via MIDI footpedal, sequencer, etc.).
As far as multiple pedals versus one big multiFX floorboard, it boils down to personnal preference. Some people like the all-in-one approach. It saves on setup time (patch cables, seperate power supplies, etc.), but it often limits you're sound. Even though these units have many different stompbox emulations, they ultimately fall victim to sounding as the design engineers interpret them, and often lack the tonal character of the originals. But again, you'r saving thousands of dollars not having to purchase all the originals, and you can usually dial-up a sound that you will like. On that note my guitarist uses
a VOX Tonelab SE, and it freakin' rocks. But seperate pedals is the way to go if you really want to design, your own unique sound (And no one says you can't mix stomp boxes AND MultiFX pedals).
