Pray the problem is software since that's all Schiit can help change. Mac's don't have a driver as far as I know so nothing to change there.
In the meantime, what I haven't heard is 'iTunes screeches!'. C-Media doesn't test their hardware against audiophile niche products. Don't expect them to rework a chipset for obscure software so that Schiit can replace a handful of boards :P
Not to be rough but I get the impression people think Schiit builds the USB>SPDIF chipset or has something to do with the driver... they don't. You should be bugging C-Media.
And it's still only affected a few % of Gungnir/Bifrost owners. Nothing is conclusive as to why it happens or how to fix it.