You need an audio/video source to do a meaningful test.
You probably have a "junk" source lying around, e.g. old VCR, DVD player, media player, security camera, satellite receiver, etc.
If not, your cable box may have multiple outputs (composite, s-video, component). Hook up one that's not used by your main system.
If not, your current capture device may have a loop-through output you can connect to the Solo.
If not, take your system down for a minute and feed the Solo from the cable box and the current device from the Solo.
Connect the Slingbox to your network and DVD player. Confirm that you can view and hear the movie on your computer or other viewing device that you have used (or will use) with the Solo. For a complete test, also set up the DVD player as a video source on the Solo and confirm that you can control the DVD player using the Slingplayer's on-screen remote.