Dear Bcollins: IMHO, the first and more important/critical subject on the addition of subwoofers in any audio system ( for music ) is to try to understand which are the different audio areas where subwoofers could help our audio system to improve its whole quality sound reproduction.
Here you can read something about that can help you:
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1117893153&openflup&27&4#27
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1117893153&openflup&31&4#31
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1117893153&openflup&158&4#158
I agree with other people in favor of velodyne.
Regards and enjoy the music.
Raul.