once you realize that all "live rock" provides in terms of filtration is surface area for bacteria colonies to grow, and the more porous it is the better because that equals more surface area, the rest is easy.
In reality of all the options available, I always thought bio-balls were rather lame. They offer lots of external surface area, but none internally and what external surface area they offer pales in comparison to the area offered by other media types.
I have grown to prefer Seachems Matrix because it affords lots of surface area externally as well as internally. It is essentially pumice pebbles.
There are lots of different similar materiel's available made from clay/ceramic that also offer lots of external as well as internal surface area.
Even a simple sponge filter offers more surface area than bio-balls.
why they continue to be used I can only figure is due to ease of access and ease of use, but beyond that there are much, much better options available.
So the point of this is that if you go this route, you will have much better success and stability if you choose a different bio-media instead of bio-balls.
You want something that provides lots of internal surface area for de-nitrifying bacteria, which plastic bio-balls do not.