One of the drivers is not working, how to solve this?

Please check first if the screws on the terminal are tightened and the bridges which connect the bi-wiring terminals are securely screwed. If that is the case and there is still no sound, please contact our support.

Am I allowed to rotate the tweeter of the 99.25 Center to use it as a normal compact speaker?

Unfortunately, we cannot allow that for reasons of warranty. Please contact our Support.