thanks for the replies. So looks like I need to set the whole thing up before I can truly know if it will work correctly.
deSilva - you say 'In the first place, no voltage should be applied to any input pin above Vdd+0.6V or below Vss -0.6V' but the reference sheet for my 4051 says that the switch voltage is 0-10V (refer to CD74HCT4051 data sheet, product information and support | TI.com)
Is that correct?