Thank you retrolefty, very helpful!
I'll be looking into ordering an external DAC then I think. I am curious though. Obviously since the amplitude is itself transmitted with a signal of varying frequency, the maximum analogue frequency that I can successfully transmit and decode will be lower. Any ideas what ball park that frequency might be in?
Also, would it be a terrible thing to program the DAC into the receiving chip? It doesn't seem like it would be overbearingly difficult to write one.