If you are going to have multiple devices communicating with your computer, you either need some ingenius timing-routine, a system where device 1 transmits to device 2, which appends it's data and transmits to device 3 and so on (not very efficient), or 2-way-communication so the computer can push/poll information to/from the device it wants.
Like I said, sending continous bits was a retarded suggestion on my side. Just send jibberish, followed by an identifier telling the computer that data is starting.
I'm not sure how you plan to link together several devices.. If you need any-to-any communication I'm pretty much lost, but if you need many-to-one type communication, getting a tranciever for your devices is the only good way I can imagine.. The computer says "Hey, unit 3, what is your analog input status?" and device 3 answers.