When I bought my DX, I bought a extended battery BH6X (1930 mAh) from the Verizon store.
Can I use the same door with both the BH6X and BH5X batteries? Or do I need to use the door that came with the BH6X and the door that came with the original BH5X as a pair?
I think he's asking if he can use his extended battery door with his stock battery? Obviously the stock door doesn't fit the extended battery, that's why the big one comes with it's own door. Using the extended door with the stock battery, however, also won't work because the battery won't be held against the contacts correctly and your phone will randomly power off from a bump.
Yup, good point, too.