To get alsasink to work with >2 channel audio, you need to specify 'channel-mask' in the caps. This requirement is noted elsewhere in the 1.x documentation, but not in the alsasink documentation itself. A note here of this would be useful.

I only became aware of this requirement when porting a 0.10 plugin to 1.x, when my multichannel audio didn't work because I wasn't setting a 'channel-mask'. I'm not sure if this is something that should have been done anyway with 0.10. Either way, this change in behaviour should probably be noted in the 0.10 -> 1.0 porting guide.