Problems with audio on New toshiba 32" TV?

just bought and hooked this up in my sons room, picture is great, sound is awful! It is like the sound is coming from a little tin box--no bass, tinny treble--we have adjusted, or tried , the bass, etc levels, they dont even change when adjusting--we've tried running it thru the Xbox, and the cable-It's an HD ready TV, but we dont have HD service. I do however use an HDMI cord on my liv room set, and it helps the picture a LOT--maybe the sound too?idk, guess I'm assuming. So we tried the HDMI cord on the new set and it didnt help at all--any suggestions??