The code you attached doesn't seem to do what you said you wanted -- instead of a sinusoid, you are generated a square wave and running it through a PID controller.
When "getting acquainted with hardware", MAX is hard to beat. Can you "see" the Elvis III if you open MAX and connect Elvis? With a real Elvis connected, MAX should give you the option to run some Test Panels, one of which is to generate Analog output (I think it does do a sinusoid, if memory serves).
If that works, then you know the Hardware is working, now "it's only the Software" that you need to worry about. Why not generate a sinusoid and play that directly into the Elvis, without the PID stuff, and see if you get the expected output.
Start simple. Do a simple test. When (if?) it works, add the next step. When it doesn't, try to figure out what isn't working (asking colleagues can be very helpful), and come back to us if you need more help.