Streaming through FM with pifm or pirjb

I use pi musicbox since about a week and i found it really useful. Im not a spotify member, i used it mainly to listen stream radio station, or local mp3 on my sd card.
Since i used in the past pifm, ive added it to the musicbox with a good antenna and i can grab the signal at about 1000 feet from my basement.

Im using command line to stream internet radio through fm :
sox -t mp3 -t wav -r 22050 -c 1 - | sudo ./pifm - 99.0

then i can hear the radio classique from France (im in Canada) on any radio tuned to 99.9 at like i said 1000-2000 feet…

If pifm could be integrated on the pi musicbox web interface so we could choose any local file or directory or web internet radio and add the frequency we could choose …

For now im looking a way i could plug my pimusicboxFM in my car and it start automatic playing local directory of mp3 on a specific frequency (i dont have other audio input in my radio, so fm transmitter is the only way)

There is also rpitx ( but ive just started looking at it … it seem more powerful than pifm
thank you for any help /inputs

You could probably setup mopidy to output to a filesink which is a FIFO, and then pipe that into the pifm binary. But there would be no way to easily switch to an other output.