You can check this by checking if the receiver has a fiber optic port in the back. If it doesn t you will need to buy a separate decoder. That is the way I went. Because when I bought my receiver they didn t have any AC-3 units that were not priced to the hill. The prices have since dropped.
Speakers make all the difference in the world.
You can have a second rate receiver with great speakers. But you can t have a top rate receiver with second rate speakers. The quality of the speakers makes a huge difference in the performance of your system. I would recommend that you spent most of you energy on finding the perfect sound and brand. I am a little biased and I am a huge fan of Energy .