I see a "Signstek HiFi USB to Coaxial S/PDIF Converter Convert Digital to Analogue Signal Mini USB DAC PCM" item that looks like it would take a usb input (from a pc) and let me get a s/pdif output - ...
I have an older Panasonic TC P50ST30 (release review/specs here) that was generously given to be by another Arsian that does have ARC support (I think). The TV sitting in front of an old but nicer ...