I had a go with XMidiCtrl and got it working to control all throttles via a slider and it seems good:
{ ch = 1, cc = 19, type = "sld", dataref="sim/cockpit2/engine/actuators/throttle_ratio_all", value_min = 0, value_max = 1 },
It doesn't seem to support arrays though, e.g. float[engines], so it can't control engine 1 or 2 separately. Am I missing something, or is this not currently implemented? I was trying to use throttle_ratio[0].
Thanks