Well you have 6 analogue inputs. If you use one for the digitising of the sound then that leaves you 5 pots you can connect without the need to multiplex anything.
If you want to see how to get more inputs then look at this project.http://www.thebox.myzen.co.uk/Hardware/MIDI_Footsteps.html
The multiplexers I use there are much more suited than the ones you mentioned in the title.
to fx. pitch or speed-up the sound
As I said the memory is very short but a simple 256 byte buffer will allow you to do pitch up and down but the quality is not the greatest because of the fact you only have 10 bits resolution on the A/D.