As far as I can see, Pinnacle Studio MovieBox HD is not much different from Dazzle DVD Recorder. The former has a firewire input/output, but many motherboards have it as well.

I will try to repeat the same thing about playing in HD while recording with SD capture card. Hopefully it will be more clear.

xbox doesn't seem to allow you to ouput SD and HD videos simultaneously using HDMI and composite outputs, or component and composite outputs simultaneously. So you need a component to composite converter or a component to S-Video converter, and I don't think it makes sense to spend money onto it.