Mac, within reason there's no "sizing" problem for speakers in typical home listening rooms such as yours. As long as you sit far enough away for the drivers in big speakers to "blend"(say 8' or more for M80s)there's no need to think big speaker, big room. You of course are in control of the sound level, whatever the size of the speakers.

As to the sub, it's doubtful whether the relatively small difference between one SB12-NSD and one PB12-NSD will be enough to bother with.

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Enjoy the music, not the equipment.