Additional Sub

Just a quick question about adding another sub to my system. I have a very large room (32 X 28 - with a tapered 9 to 12 foot ceiling) and my Klipsch KSW-12 needs a little help. The Klipsch is placed in front of a bare wall - which works well with it's rear port. The additional sub will be placed in front of a wall with heavy drapes. Keeping in mind that I'm trying to keep the output power as close as I can to the Klipsch - would it be better to purchase a down-firing FRONT PORTED sub (like the Athena AS-P6000), or a front firing sub (like the Velodyne DPS12)? Or does it make any difference?

My equipment:
Pioneer VSX-74TXVI Receiver
JVC XV F80BK DVD Player
Music Hall MMF-9 Turntable
Nakamichi CR-7A Tape Deck
Polk RT1000 Tower Speakers
Athena AS-F2 Tower Speakers
Energy C-R1 Rear Channel Speakers
Klipsch KSW-12 Sub

Thanks, pthoth