I'm putting a Digitrax SDH164D Sound, Motor, Function Decoder into a small HO tank or switcher loco. The problem is the size of the speaker, it's too big. I think I can fit a smaller round one in the boiler, but which size will give me the best sound? Soundtraxx sells an 8 ohm 3/8" round speaker, about the smallest I've seen. They have others that go up to 1.56 x .78 inch oval too. But how do they sound? I realize the 3/8" round isn't going to sound like a surround sound stereo, but what can I get away with? What size/brand of speaker is the best? DCC without sound is like bread without butter.