[mythtv] Digital audio passthrough

[mythtv at meric.id.au]

> The easier alternative for you was to simply set the passthrough
> device in the advanced settings. Why didn't you use this approach I
> suggested earlier ?
> 
> What do you mean in the ticket?

I'd gone off on a tangent based on a belief that my current issues were
somehow related to the use of the alternate passthru device, so I
started trying to figure out why I needed it in the first place.  It
wasn't until I fixed that and still had issues that it dawned on me that
perhaps my sound driver was stuck.  I guess it wasn't that obvious, as
in the past when it has failed, all audio stops.  In this case, it would
pass PCM, but nothing else.

I'm currently running on stock myth code, using the alternate passthru
device and everything is working as expected.  If, at some point you
change things to remove the iecset code and set the flags in the device
name, my (and perhaps everyone else's) need for this setting will
vanish.

Richard.