On this schematic, I'd like to replace one of the DIP switch with a 3-way switch that connects only the x3 or only the x6 or only the x8, as I only need to implement these positions. What kind of switch should I use? The tiniest possible as it's to add to a musical instrument.
A three-position wafer switch (rotary action) would be the usual choice; DIP switches are perhaps smaller, however. As I read the diagram, one should never connect multiple Q (output) nodes together, and the DIP switch does not lock out that possibility. It seems you'd want a three-position (SP3T) switch? Or, to keep things simple looking, one ten-position and one three-position (SP10T, SP3T)?