Probably the most direct analogy you could build (of the original RM=radio music firmware) would be to use the Raw Player.
You can set up your “stations” by selecting the sample using “Select From Pool” and then “Enable Multi Select”. Choose all the wave files that you want to represent your “stations” and hit Enter, and the 301 will automatically create a wave file in RAM that concatenates and pre-slices all these wave files. Default mode for the Raw Player slice control should be “indexed” which is what you want. Adjusting the “slice” parameter by enough (1 divided by number of slices) and fire a trigger into gate will switch “stations”. There is also a “start” parameter which you can use to offset the start position when you reset - similar to the start knob/cv in on the RM. It only goes up to 5s but you should be able increase this by putting an external offset into the subchain and giving it a high gain (say using a rational VCA in addition to it’s built in subchain gain of up to 3).
This should be very CPU friendly. But a big difference between the Radio Music and the Raw Player is that the Raw Player keeps the wave file in RAM, the RM reads direct from the SD card, I’m pretty sure. There’s a pretty good bunch of sample RAM available but if you’re talking about really, really long samples, RAM is more the resource to pay attention to than CPU. There is also a Card Reader unit in the 301 but it doesn’t support slices - so you’d have a single “station.”