Graham,

Much of this will depend upon the mic you are using and if the impedance of the input system matches that of the mic. If everything matches up pretty closely, then an impedance matching transformer adapter is not necessary, and it can sometimes cause problems.

If the output of your wireless receiver is going to the keyboard's line in then nothing more is needed. Most of the wireless systems are line out voltage and match up just fine with any line in system.

Hope this helps,

Gary