Graham,

There are a lot of ways to go with this. If you have 3 vocalists, and three mic channels with effects, I would fire the output of the mixer into the keyboard's Line/Mic input connection, which is what I do with my outboard vocal processor. This provides you with the ability to raise and lower the mic volumes independently, or just raise the overall volume using the amp's master volume. I would mount the mixer on the right side of the keyboard where you have instant access. I would NOT run everything through the mixer--just the mics and any auxiliary equipment such as an MP3 player or laptop audio output for playing MP3 or WAV files.

As for recommending which mixer to use, most of those mentioned above will provide excellent, high-quality vocals when used with high-quality, super-cardiod or hyper-cardiod mics. Of course, individual effects will have to be selected to suit your singers.

Hope this helps,

Gary