I studied and made blackbelts in four different arts befor I was able to learn JKD As it was not readly avalible back in the early 70s Have done some boxing hands to. But with JKD I gave up alot of the other styles. And train mainly JKD. And do as seperate mix. But JKD by its self Has plenty to train. Though some arts may blend to use. Thats a personal mix. But JKD is JKD. I like what it has done for me. So why add to it . Keep that part seperate and as a personal mix. Theres enough in JKD to take what is useful. I do though think it helps if you have prior training befor you start JKD to have a better understanding. But each there own.
Cant say I actually take supplimentary classes. I listen and train with others but generally I look at where my weakness is and try to fix it through various forms of research. This may include asking someone from another class. So although I could say I do various things I feel it would be misleading as I do not go to anyones classes. Unless of course it is a one off visit to a new club that interests me. Like I am planning to go to a MMA class soon, although from reports so far I probably wont join up. You got to be pretty well rounded for me to be your student.
It almost sounds a little arrogent as I write this. But I still can not help but not enjoy going to classes where they treat the student as stupid and apply stupid restrictions to training and especially because most classes are too fitness orientated. That is for home, the class is for technique.