It seems that you are having some issues in order to send the signal out to a HDTV.
Firts, we do not provide support for this specific configuration (out from computer to HDTV set). And even though you can try it out, the Slingbox and the HDMI cable are not compatible (no matter which Slingbox you own), due to the HDCP restrictions.
The following link will provide you with further information about this specific situation.
To be honest, I'm struggling to understand this having read both the link and the post above.
Can you confirm if the following setup will work, or not?
Slingbox Pro-HD connected to set-top box HD output via component (since this is the only method as Slingbox Pro-HD has no HDMI input)
Slingbox Pro-HD connected to Internet/Network
Mac laptop connected to Internet/Network
Mac laptop running Safari Slingplayer Webplugin in full screen and set to stream in HD
Mac display port connected to TV HDMI in (via adaptor)
Is it the case that the above will work *until* the set-top box HDMI output is connected to the TV at location 1, which then might interfere with the set-top box component output to the slingbox?