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You appear to have already made your decision, but one perfectly legal way to accomplish what you want to do is to use 802.11 wireless over an intranet. You can use an inexpensive internet radio receiver at your transmitter site to capture the stream. There are some internet radios out there that can use battery power and almost all use DC. You can easily achieve several hundred feet distance (legally) by using directional antennas at your home studio, pointing to the receiver.
I used this method once when mounting a transmitter well away from the studio. I put an older Roku internet radio in the weatherproof box along with the transmitter – I did have access to power (but did not have to worry about running hundreds of feet of audio cable).