As far as connection is concerned, wireless mic systems come in two flavours. Those that convert the signal to "line level" and those that maintain it at "mic level". The info from your post doesn't give enough detail to say which yours is. You'll have to read your manual and decide for yourself which type you have.
It breaks down like this...
Cabled microphones put out a very weak signal. It's too weak to connect to an AV amp directly. There has to be another box present (a microphone pre-amp or mixer) to boost the signal level so it's a similar level to other devices such as a DVD player, Sky box, games console etc. Without a microphone pre-amp or mixer then if the AV amp works at all then you'll have to have it on full volume and there'll be quite a bit of background hiss. That's not good for sound quality or for the life of your amp.
Microphone mixers come in a variety of sizes and price ranges; anything up to and over £5000. But here is a little mixer for under £50 that'll do nicely for you.
Behringer
The other advantage of a mixer is that it allows one to change the tone of the sound as well as individual mic volume, pan position (left, centre, right) and master volume, and also to mix in sound from another source such as background music from a CD player.
If your mics have a wireless receiver that also doubles as a mic pre-amp then you can connect directly. Just get the appropriate adaptors from 1/4" jack to phono and then connect to one of the Yamaha's line inputs: CD or AUX which might be labelled up as Audio 1 and Audio 2. [Don't use any socket labelled Phono for anything other than a turntable input].
Even with mics as described immediately above, you might still find the Behringer mixer useful. It has line inputs as well as mic inputs so works equally well with either type of connection. Although the Yamaha has the usual tone and balance controls they don't have the sort of flexibility to tailor the individual mic sound.
