One of my MR8's has only its tweeter working, im guessing the bass driver might be blown? How can i test this though and be sure it is the bass driver and not just a simple electrical fault?

I replaced both capacitors and only now my tweeter is working , i tested it with another mackie amp cabinet and the woofer works fine so there is something bad in the bass amp , it was buzzing why i changed the capacitors and i changed them 2 times to make sure it wasnt a bad capacitor and only my tweeter works there has to be something else wrong in the amp board

Open the unit and remove one wire from one of the woofer terminals and using an ohmmeter check the resistance between the terminals. It probably should be between 6 and 16 ohms... they don't give the specs on the speaker... if it is very high or infinite resistance, the voice coil is blown and you be re-coning or buying new speaker. These are close in speakers and intended for a small room for studio listening while mixing. If the speaker is OK, then the bass amp in the cabinet has a failure... pray, as that is cheaper to repair than a speaker.