I run my 350 with a sleeve on it and nothing inside the container. I find that it gets clogged quickly if I fill it with carbon or bio material. My 350 runs on a 42 gallon tank and only needs changing every month or so. When I ran carbon in it I had to service it almost weekly. The carbon container does grow bacteria nicely, I just change the sleeve and leave the container alone.
I think you will need to keep an eye on the 350 if you load it with bio balls. I think it could work but you may need to clean it out fairly often which might defeat the purpose of what you are trying to accomplish. You really don't want to ever have to clean bioballs if you rely on them for a major portion of your bio filtration. I have seen that you can hook up bio wheels to the 350, maybe that would help you out bio wise?
Hope this helps, good luck.