Digitally Switching a Single Source into 128 Channels
How about something like this:







simulate this circuit &ndash; Schematic created using CircuitLab

Essentially a Pass Gate (aka Transmission Gate, aka an Analog Switch) per channel. That's an NMOS and a PMOS transistor and you'd want to ensure the were complements of one another, and you'd need 256 control signals, 128 NMOS transistors, and 128 PMOS transistors, but I imagine this would probably be your lowest cost approach if you really need to do what you've described. You'd obviously need to incorporate some sort of FGPA or CPLD or MCU with a lot of I/O expansion to get the control signals, and a custom PCB of course.