In the case of the Pace DTVA, I believe this unit actually has a viewing card slot which *may* be upgradeable so you could in theory just insert a TOTV viewing card witout purchasing this CAM. The CAM gives you a slot to insert the viewing card into, if your box/TV doesn't have a suitable slot already
Of course this has not been confirmed, if you have one of these boxes I would sit tight and see what transpires.