I managed to get my hands on one of these not so long ago, and still got him, they're great turtles but if oppurtunity arises they will eat fish... I had a weak pleco in the tank and am sure, to this day, that it was the FRT that finished him off, having said that i wouldn't ever sell him for the life of me, he's the main focus of my aquarium...
His standard diet is:
Kiwi and banana stuffed with reptomin
Hikari massivore (if he gets them before the catfish)
Algae wafers
Any frozen food big enough that he gets to (prawn, mussel etc)
Edit:
Me and my friends were fairly successful at keeping small soft shell turtles up to about 6" shell with large community fish as they are too slow 90% of the time to catch them, BUT they will try (hence why it only worked in tanks with quick large fish) and in hindsight i wouldn't recommend it as they also need basking spots (we did this with floating piece of cork) and UV spots.