Help! Problems with my 800rb rig

[Ohmaigawd]

For a while I have biamped 100w to an ampeg 4x10 and sent the 300w to a 15 below.after about a year of this the 15 i had stopped working, i figured it was old and carvin so it was no big deal. Just recently I purchased a gk 15inch cab with an ev driver and I played it in the same manner and all it did was distort and not handle any low end before it stopped working and it stank like something burned. I just had my amp serviced a few months back and it runs my 4x10 full range fine, what is my problem? is this common? everything was 8ohm.....is there certain cautions to be had when bi-amping?

any help would be greatly appreciated, even if it is a better place to direct my question.

Thanks