Hi, Tony, and welcome to the forum!
The Marantz 5003 will upconvert component video to HDMI, so you could do what you want to do with the Wii.
Just a thought - your TV has enough inputs to handle the video connections directly. If you wanted to keep the Denon 2802 for a while, you could just route the video straight to the TV and route the audio to the receiver. One downside is that you'd need to switch inputs on both the receiver and the TV when you wanted to watch/listen to a different source, but if you have a learning remote that runs macros (or are willing to get one), you could switch both the receiver and TV with the push of one button. Another downside to the 2802 is that it can't handle the latest lossless codecs unless you use the 5.1 analog inputs, but your blu-ray player doesn't have those outputs. From what I've read, the improvement over Dolby Digital or DTS is arguable at this point, though.