Couple of things look mysterious on that drawing:
-4051 switches one input to eight outputs (or other way round) on your schem there´s just one signal in and one out? What do you want to achieve with that?
-4051 has three control inputs A,B,C. You can of course control them with a stream of gates, but it would only change one single bit from high to low, you need three streams to cover all eight switching options.
Please ignore me if I have misunderstood something vital, it happens

Also the Lunetta section on electro-music.com houses some posters with very good knowledge
about "analog" digital CMOS, etc. in a synth context!