I am answering because I see no one else has. I don't know the SPL-14 at all, but I own the DD-15. I think it's the adjustments on the TV monitor with the microphone that make it an exceptional subwoofer. You could also consider getting an SMS-1 to use with your existing sub. That way you would almost have a DD-15. Again it's the built in SMS-1 feature that I feel makes the DD-15 so great.
