Looking on the Nuforce site at the W-1, not seeing any specs on ins, outs, etc. and no pics of the rear panel. Can I safely assume that it has speaker level ins and outs and the xover functions on those so I can just feed the sub, then crossed over output out to the mains?
No, the rear panel only has line-level inputs (and outputs), so I assume the monitors would have to be run full-range.

The specs of the Dia say there's a separate line out for a sub but I'm not seeing it in the pictures. Using it that way would also then still force the small mains to run full range.
The Dia references a line out to be used for a subwoofer, but the only line out seems to be the 3.5mm line out on the FRONT panel, which seems a bit wonky.
Also on the subject of digital optical out from your TV, my Panasonic plasma (and some other Panasonic models as well) don't have a setting to output 2 channel PCM instead of Dolby Digital. In fact on my TV it states:
"When an ATSC channel is selected, the output from the DIGITAL AUDIO OUT jack will be Dolby Digital. When an NTSC channel is selected, the output will be PCM."
So just make sure that your particular TV can be set to always output 2 channel PCM.
Steve