Brett, have you gone completely though a trimming chart?

http://www.rcaerobats.net/trim_chart.htm

A lot of times the couplings can be removed from other adjustments. I use mixes as a last resort for this reason: say you use a mix to fix your knife edge coupling, which will be slaved to your rudder. Every time you use your rudder (unless its a switchable mix) you will be using the mix. Maybe you don't want elevator and ailerons when you do a stall turn? I'm not saying not to use a mix, but go over your plane with the chart and see if there is another correction that needs to be made.

There is no knife edge flight in the first two classes of pattern or IMAC.