Trying to get live strings and vocal in linuxsampler, i was suprised by fact, that this controller doesn't have effect (with all engines and banks, including suggested for fluidsynth), but with fluidsynth all ok. It is not clear now, how this controller should be handler at all. I expected, that it should be same as for velocity, but set for enter channel and variable, unlike V, specified for notes and constant). I searched both in fluidsynth and qsynth sources to see, for handling code, but found in fluidsynth only two constants (EXPRESSION_LSB and EXPRESSION_MSB) and command, setting these parameters to default value (127). IMHO, it is very necessary for linuxsampler, and who knows, what is not done for fluidsynth. Looks like LS devs left it for user (using qmidiroute, mididings or sequencer's builtint converting capabilities if available). This link only confirms that: http://bb.linuxsampler.org/viewtopic.php?f=6&t=207