Pre-programmed Q-Link controls over Song Mode. At least this, if HD Recorded (or imported) long files can played aside sequences only in Song Mode. Programmers definitely didn't thought those users whoes want to perform some parts of a track, and other parts want to just played back from disk, like long evolving synthesizer sounds.
Another option would be the 4th type of program, like 'STATIC' or something, wich is not loading into the RAM, instead just playing them directly from the disk. (of course, these would be really static programs, so they can't be processed, playing would be the only action they can do.)