It's great to see your efforts to adding better support for surround plug-ins. I'm having a problem with the VST2 wrapper, though, and the number of input and output channel defined by the host through the setSpeakerArrangement opcode seems to be disregared in the processing.
const int numIn = cEffect.numInputs;
const int numOut = cEffect.numOutputs;
const int numIn = busUtils.getNumChannels(true, 0);
const int numOut = busUtils.getNumChannels(false, 0);
it seems to work. Is there a reason for not using the channel counts defined in setSpeakerArrangement?