What is the optimum size for a subwoofer? current system Boston Acoustics Center MRCB micro, Boston CR67 100 watts front, CR57 75 watts rears, mostly easy listening and movies. Yamaha RX-V461 AV Receiver. I have a old Sony 8" subwoofer but have finally moved up to a LCD widescreen and am wondering if another sub would improve the sound for movie watching without having to turn up the volume. I know my system is basic but it meets my needs.