Here i want to demultiplex bit by bit where as the channel consist of 16 bit(8 for the first channel and 8 for the other) and the way the bits are is first bit from one channel and second bit for other channel and so on...
And now i want to separate it to get bits of respective channel using the technique above. The problem there is how the D-flip flop provide the switching mechanism to the SIPO registers so as to acquire the respective bits..... help me please!!!

 

Just do the same thing you did at the transmitter, only in reverse. Use a 16-bit SIPO and just pick off every other bit to one channel and the rest to the other channel.

You still have to deal with synchronization, but you have to do that no matter what you do.