If the information on my itunes is correct, than David Lucas Burge's course was released in the year 1999, making this course at least fifteen years old. While most of the course is perfectly fine to use, and will be for a long time, Burge's suggestions on synthesizers are a little dated.
It is worth pointing out that there now exists a number of electronic musicians who do not play instruments, but largely focus on composition, sound design and production. This, obviously, is a result of the digital boom in the past few decades.
So, to those electronic musicians out there who do not have a primary instrument, allow me to give you a few suggestions on what to use:
1. Kontakt or Stock Piano Library. This one is a little obvious. But if your midi controller lacks its own piano sound, or you don't like it, than it is not a bad idea to use a library from your daw or from Kontackt. I would also recommend this to someone who someone who plays something like a flute but wants to use the keyboard exercises. Using a library with your primary instrument may be a good alternative.
2. A Single Sine, Square or Saw Wave. Burge suggested that, if there are no piano settings on your synth, which many synths do not, than to use a single sine wave for training. This is not a bad idea, however I would argue that you could also use other wave shapes such as a saw or square wave. The key is, make sure it is something that you use frequently.
3. A Common Sound That You Use. If you have a particular lead or pluck that you like using, such as a super saw, than it is probably not a bad idea to use that sound. Just be sure to have little to no detuning in your patch. In fact, outside of some reverb or EQ, I would keep the patch as dry as possible. But whatever you use, be sure to save it so you have a constant sound to work with when you are starting your ear training.
Those are my suggestions to using modern tech when studying perfect pitch.
See you soon.