FWIW, I work in a performing Arts Center and we ran frequency scanners in order to set up our wireless microphones, wireless intercom headsets, wireless routers for soundboard and light board. Even after doing this our wirless intercom headsets will have issues every so often. And the distance does not matter, I have been within 10 feet of the headset transmitter and had it give me a lost signal msg. For an indise venue, where a band could be running wireless, mics, DI's IEM's and the house could be running wifi, and wireless routers on digital sound and lightboards, you should be sure the frequency you plan on using does not have traffic on it already or run the risk of having dropouts, crosstalk or just plain not working. the airwaves are more crowded that you think. Outdoors can be better but there are other things to deal with. Had a buddy doing a large outdoor festival in a waterfront park. Then as part of the event,the Coast Guard and Navy docked some ships. All his wireless just went away, gone. He had to go to wired on everything. Microwave dishes for TV transmitting, Live TV crews, Cell phone towers....All the stuff we use has adjustable frequencies so we can move if we run into issues. And of course, that adds to the cost. I think Shure makes a transmitter receiver combo that accepts line level signal. Plus the ones already mentioned. If you want quality be ready to pay for it.