(HYPOTHESISING)If they directed it at the front of the car where the alarm is most likely to be and had it calibrated so that it created a small field but a strong enough one to fry the systems and alarm then it is possible but I think it depends on the amp. If it uses mostly analog components...
I have never actually seen an EMP used for that but I was discussing it with a friend of mine who says that whenever he uses a certain function on his handheld ham radio it emits a low strength EMP and confuses the power supply on his computer and makes it reset itself. Basically what an EMP...
The MTX (I'm assuming) 81000d is a great amp but the downside is how power hungry it is it takes a lot of current and you have to run 1/0 ga. cable for it, but as long as your car can handle the load $440 is a pretty good price for it.