Looks like a job for analogue multiplexers.
A good start is this file:-
http://www.google.co.uk/url?sa=t&source=web&cd=4&sqi=2&ved=0CDQQFjAD&url=http%3A%2F%2Fwww.intersil.com%2Fdata%2Fan%2Fan1034.pdf&rct=j&q=analogue%20multiplexing%20and%20matrix%20%20switch&ei=lrxaTaShNYnQhAfsnsGzDQ&usg=AFQjCNHeKNGmRr1r5--ARM09Ey7QOx1zGg&cad=rja