David, I'm going to assume you are using HDMI for both the PS3 and the direct TV. I believe the Wii comes with a composite video/audio cable. If that is what you are using, you should be able to plug that into the composite GAME in on the back of the Onkyo and you're all set.
If you have component video cables for the Wii, then I would use that (better resolution than composite). There are two component in's on the back of the 607, one is marked DVD/BD (IN 1) and the other CBL/SAT (IN 2). You should be able to use either one and then relabel the input on the 607's internal setup. Whichever one you use, you want to use the corresponding analog audio inputs - since the analog audio isn't assignable. So, if you use the Component Video in's for the DVD/BD, you'll want to connect the audio to the DVD/BD audio in's. Likewise if you use the Component Video in's marked CBL/SAT, you'll want the audio in's for CBL/SAT.
Doesn't matter which component video in you use as long as you connect the audio cables to the corresponding audio in (then just relabel the input on the menu to Wii or whatever).
Mark
Aperion Audio Guru