PeterH:
Where is the data ultimately coming from? If it's being acquired at the PC then I would be inclined to have the playback controlled there as well, and write a small PC app that just pulled values from the data file in whatever format you chose to store them, and wrote them to the Arduino serial port; the Arduino sketch would just take data sets from the serial port as they arrive and write them to the DACs.CSV would be a reasonable choice for the file format and also for the Arduino serial comms, unless the data is already encoded in some other format.
Thanks for the input. I have a CSV of the data that I want to put into this thing, on my PC, that's where the data is from. I only have to put this one data set in, there's not currently a need to pull in other data sets on the fly. Originally it was from an engine but that part's already done, it's a nice 1200x4 CSV of data at one second intervals.
What you're suggesting was one of the options I originally mentioned, and it's still on the table. The reason I'm hoping to do it on the arduino standalone is because this thing is going to be sent out and used elsewhere and I'd prefer not to have to install arduino software on whatever computer it's being used with. It seems like doing that will be feasible with progmem, just have to figure out the best way to get the data into the arduino.