Reply to thinking of buying a midi-fighter some questions though

i am looking at a midi fighter and have some questions about the additional inputs.

With the 4 analog inputs you can add buttons knobs faders and switches but for the 4 digital inputs what options do i have there.

is it possible to connect a device to turn the digital input to a analog input or many inputs.

I was also reading that you could run a serial device to split up the digital inputs what is this and can anyone explain how it works.

Sorry about the dis-jointed post but i am having a lot of trouble finding out information about the insides of the midi fighter.