Does the new yamaha receivers support the ac3 sound?

Hi.

I thing to buy one of these Yamaha or Pioneer receivers and i want to know if they support AC3 decoding because if don't support how i can hear the mkv, avi, m2ts movies that it has ac3 sound?

And i thing to connect the wd tv live 2011 or the netgear ntv550 hd media players to this yamaha receiver.

Please tell me what will happened if i try to play one video file with only ac3 sound?

I hear it multi-channel from the receiver, i hear it only stereo, or i don't hear any sound from the speakers at all?

And why that thing happening?

Why NEW models of receivers doesn't support old audio codecs and support ONLY new audio codecs?

What can i do to can see and hear movies(Avi, mkv, m2ts) files thath as ONLY AC3 SOUND?

A LOT OF THANKS FOR YOUR ANSWERS AND YOUR TIME.

I don't say that doesn't support dd and dts decoding i tallied that doesn't support AC3 decoding....

Look the links i gave above and you will see that either a/v receiver support ac3 decoding only dts, dts-hd, truehd.

Is there a program that i can convert any mkv file that has inside ac3 sound to pcm.

I home mkvtoolnix or tsmuxer can to that and if it doesn't please tell me one program that can do that so i can hear the ac3->pcm into these receivers.