Ah okay. I think I know what you're getting at now.
You want it to autotune to the strongest signal that has a TA whilst still playing your MP3s?

It could be done in hijack I think. It would be quite complicated as you'd be fiddling with the tuner without the player softwares knowledge. So you could end up in a funny state depending on how the player tunes. The commands are all detailed in this thread. It's a little way down the page. I think the RDS AF is done using the set freq B commands from what I remember. May or may not help in this case.

- Trevor