The wii has two options for video, and only one option for sound.
Depending on if you are using Component cables or Composite cables.
These are the Red, Green, Blue for video, and Red and White for sound.
Your amplifier, as far as I can see from the PDF, does not have the ability to do component video. If you're using component, you simply plug the RGB cables into the TV, and the Red/White sound into the amplifier at either, VCR, V-AUX, DVD, and D-TV/CBL.
To get it playing, your amplifier will need to be turned onto the correct input for the wii, as well as turned onto the Composite channel.
In this case, you plug the Red White and YELLOW into either, VCR IN, V-AUX, DVD, and D-TV/CBL. (Ignore VCR OUT)
THEN you have to run another yellow cable from the Monitor OUT port on the amplifier into the TV.
This will allow you to switch between multiple units if say, you have another DVD player or something like that in the amplifier. If you do this, your TV will be turned onto, say, AV1 for example, and then you switch the amplifier between DVD/VCR/V-AUX etc to change between Wii and DVD player.
If you're still confused, please let me know, but it is relatively simple as matching red - white (only that you SHOULDN'T plug into is the OUT terminals, as well as the 6CH Input - this is only for surround sound DVD players, the wii doesn't do this. If you want surround sound, your amp should still be able to play stereo surround from the wii using the method I explained above).