I also recommend the AKG, the handheld microphone I use all the time is the D5, and they have the wireless version of it, and one thing, they use only one AA battery that last so long, my Friend Bob Roppolo use it all the time, and he told me that sometimes he goes over 8 gigs before he needs to change it, and never had any trouble with it over 5 years now....besides, is Super cardiod and that is less likely to get feedback unless you are if front of the speaker unlike the just Cardiod pattern microphones like the one you use.....
WMS420 is the model you want to see.
http://www.akg.com/pro/p/wms420system