You can control external MIDI controllers. For example: SunVox sends any MIDI commands (note on, note off, control change) to some hardware synth.so as for the midi upgrade, if i'm reading the 1.6.2 notes correctly - you can control any parameter of any device using knobs on a midi controller that are all set to cc80 or...?
But the hardware synth (or MIDI keyboard) can only send Note On / Note OFF to SunVox. At least in v 1.6.2 :)