I have an older XM radio, that broadcast a block on its own! XM Radio really needs to be processed, so you need an external transmitter. Be careful not to rebroadcast the channels with the four letter words, it won't be XM; you will have to worry about!
I have had good feedback, from users of the FM100b. Using a well tuned outdoor antenna and some distance from other antennas, will eliminate many problems you are encountering with images on 146.520; often caused by overload.
Make sure you use quality RF cable, poor quality cable from China can cause high SWR. I got some fake Belden from a reputable business, on some frequencies; I would get 2.1 to 3.1 into a dummy load, but that was only after spending hours trying to tune an antenna.
Poor processing, can cause that off frequency sound. FM, is very sensitive to excessive highs; even with a good LPF.