Re: Everything through HDMI output?
Tough to say what would be your best bet.
You speak of adding speakers, do you plan to (eventually) go to a 5(6,7).1 setup?
If not and you want to stay stereo (two channel) and you want to integrate audio/ surround sound then a receiver will do just that. Price runs the gamut, from a few hundred dollars to thousands, and the video transcoding is available at all price points (pretty much)
As for the Wii, does it offer HDMI? I don't know either way, but I would warn you to get as broad an HDMI switcher as fits your budget. Saving a couple dollars for one less input isn't wise if you ever plan to upgrade....
Ken Taraszka, MD