OK - which input connectors are you using for the radio mic and fiddle?
If you're using the jack sockets for those, and the XLRs for all the other mics and instruments, you have 20dB less gain available on the jacks and that would account for the low levels on those two channels.

Your ipod is best connected to a stereo pair of line inputs e.g. 9-10 or 11-12 etc. and should not overload those. Set the button for -10; that's "consumer audio" live level, the +4 setting is for professional audio line level. Or you could use the CD/TAPE phono (RCA) but you won't have any EQ controls on it if you do that.

If you can set up using the PFL (called "solo" on that desk) buttons so the meter readings are about the same on each channel, they should sound about the same level in the mix. You should set the main faders to 0 (that's about 3/4 of the way up) use the master fader to set the approximate overall listening level, and then you should be able to get a decent balance by adjusting the main faders no more than +/- 10dB.

Anahata