Get the new Slingbox 500 . That is the only way you can connect 2 HD sources. The Pro-HD (I assume that is what you mean) can connect to only 1 HD source.
And I should point out that if you used the DirecTV box to drive the HDMI input then you would not be able to stream any protected (HDCP) content.
Thanks for the information. I've been reading about the Slingbox 500 and at first glance it seems the ideal way to have two HD sources for use, having both an HDMI and Component inpus for HD usage. The problem of course, as you pointed ou,t is that the broadcasts protected via HDCP will not let you stream any of their content via HDMI to another source such as a laptop. This renders the HDMI connection virtually useless for HD content since much of it, and likely even more in the future, will be HDCP protected. In light of this fact, Slingbox should have provided two Componet inputs to be able to use two HD sources.