6 Months is probably the very beginning of recognizable "babbling" sounds from a baby. You'll probably begin to hear patterns. I'd consider it different than cooing sounds. He's probably just starting to realize that, "Hey, this is my voice. I can control it. Cool. Let's scream during dinner."
On the subject of language:
My wife stayed home for the first 18 months of our daughter's life. At that point she was talking, but only in a way that her mother and I could understand.
We decided that it would be best for her to go to a day care at this point since she really loved being with other kids. After a LOT of research we settled on the Foreign Language Immersion Childcare Center (FLICC). They speak only Spanish to the kids.
Within a month (I'm not kidding) her language skills grew enormously. She began to speak (English) in complete sentences. Most likely this is because there were kids a year older than her in the class who had better language skills.
She's 4 now and is still at FLICC. She speaks clear and articulate English. She can speak Spanish and can translate for us in some cases, because neither her mother nor I speak Spanish.
My point is this: kids learn best from other kids (sometimes not exactly what you want them to learn
). That is one of the main concepts of the Maria Montessori schools. Not to say that we, as parents, don't have a lot to teach our children; but put a kid in a classroom with kids a little older than he or she and watch what happens.