Hi John,
I've never attempted this configuration, but it might not be too difficult to get it working. If I get some time this week, I'll mess around with it on my Beagle Bone.
I think that you might have to do something along of the lines of:
1. Set enable 4 tx serializers in your McASP0 node:
&mcasp0 { pinctrl-names = "default"; pinctrl-0 = <&mcasp0_pins>; status = "okay"; op-mode = <0>; /* MCASP_IIS_MODE */ tdm-slots = <2>; /* 16 serializer */ serial-dir = < /* 0: INACTIVE, 1: TX, 2: RX */ 1 1 1 1 >; tx-num-evt = <32>; rx-num-evt = <32>; };2. Modify asound.conf to properly identify the 4 TX elements in McASP0 in user space (this would be up to you how to do based on how you want to playback to work). The Sitara Linux SDK Audio page has some info on this--look in the ALSA user space interfaces section and the TDM example in the debug section.