Current Source version of TLC5940 (current sink LED PWM driver)?
I'm more of a hardware person rather than software, so I immediately look for hardware solutions.

My approach to this problem would be to have a single AC signal source followed by several digital pots.  Each of those digital pots is followed by an appropriate buffer or power amplifier that then feeds one actuator.

You can generate the signal either using a single PWM output from the controller (appropriately filtered) or with any of the very many analog hardware techniques that are available.

You will need to decide how much amplitude resolution that you need.  You should also find out how much amplitude variation you need - does it have to range all the way from zero to maximum amplitude or does it need to vary only a certain percentage of the range?

Both of those questions will determine how many steps your digital pot needs to have.

If it turns out that you need extremely fine resolution, you may be better off using a multiplying D/A converter instead of digital pots.  Such converters can act as digital attenuators and they are available in bit sizes up to or exceeding 16 bits.  You would feed your AC signal source into the D/A reference and the code word that you send into the converter determines the output amplitude.

Both of these techniques can be fairly inexpensive.