For MPX, there isn’t — and it would be pointless. MPX would use so much bandwidth, and if you have a computer at the transmitter site anyway (to serve as the other point), you might as well run the processor on that computer instead, and run MPX directly to the transmitter.
For MP3, it probably exists — I don’t know of a suitable solution, but I will keep my eye out.
You should be able to achieve 1 or 2 second latency over the internet — but I wouldn’t run latency that "low" as it would easily drop out. Better to run 10 second latency and have some protection against buffer underruns.
There is a reason why Shoutcast has so much buffering — the internet simply isn’t reliable enough for audio otherwise!
Best,
///Leif