Have you got any where with your issues yet?. Is there a loop amp in the hall at all as these can cause issue and cause feedback it close to mic cables. check your gains. and your eq on each channel. Also you could ring out the feedback with the yamaha graphic. I am in Hertforshire way, if you want your system looking at i would be happy to do so for a cost. I could give you some ideas and reccomendations for a new system and potential suppliers. I work as a full time av technician and have designed and install systems for people.
