A high-quality dimmer pack will have chokes to reduced both acoustical and electrical noise. This is done by the choke increasing the rise time (dv/dt) of phase-control edges. That should help your problem considerably.
As hbiss said, these problems can sometimes be quite involved. It's important that grounding and shielding of the audio system be done correctly.
Something that comes to mind is whether you have professional or amateur audio equipment. A lot of amateur equipment uses unbalanced connections between equipment, which is quite susceptible to noise, especially ground and neutral noise from the power system. All the connections between components, and from the microphones, should be balanced--that is, with a plus, minus, and shield connection. These are usually carried on either XLR or Tip-Ring-Sleeve type phone plugs. If you have any RCA connectors, or Tip-Sleeve type phone plugs, you may have problems. (I hope I'm not insulting you by explaining this. Also, the vast majority of church systems are pro-grade balanced systems, so this probably isn't the problem. But... it never hurts to check out the obvious.)
The dimmers in my church are fed from a 200A feed to two ETC dimmer packs, and an additional 100A feed to a third dimmer pack. So I'd say the 200A they're looking for is within reason.
[This message has been edited by SolarPowered (edited 02-23-2005).]
