Oh. In that case, xsplit can definitely do it. Just get two capture devices, hook them up to the same computer, and make them separate scenes in xsplit. Both capture devices get initialized, so there's no downtime when swapping between scenes (except transition time, which you can disable anyway). I think wirecast can do it, too, but I'm not sure how to do it there, and I don't think wirecast takes the HDPVR as a camera source, so you'd have to use BMI Pro/Shuttles or other capture card/devices (like Avermedia ones, etc.)
It'd probably work best with two Shuttles, anyway, instead of a shuttle and hdpvr, due to possible differences in lag time between devices and somewhat flaky support for the HDPVR as of the latest xsplit patch. I'm also not sure how xsplit sees multiple HDPVRs, so there's that problem as well.