Four channel output with ChannelMergerNode

Hi all,

I've been trying to get a DJ app style 4 channel output (1 stereo main, 1
stereo cue) test working in Chrome Canary. I get audio out for the main but
nothing for the cue channel.

Code I'm trying out:

ctx = new webkitAudioContext();
ctx.destination.channelCount = 4;
merger = ctx.createChannelMerger(2);
merger.channelCount = 4;
merger.channelCountMode = "explicit";
merger.channelInterpretation = "discrete";
merger.connect(ctx.destination);
 main = ctx.createGainNode();
main.connect(merger, 0, 0);

cue = ctx.createGainNode();
cue.connect(merger, 0, 1);

I've checked the hardware using a couple of other programs and that's
working so I don't think the sound-card itself is broken.

Any suggestions on how to debug this would be greatly appreciated.

Thanks,

Michael