Acoupower

i sold my harman kardon 5.1 system and now have some spare cash and dont have a center to go with my 4 polk monitor 70 towers. i have been told by MANY people that i should match and go with a polk center speaker. my sub is pretty loud so when i would turn up my system the center would kind of fade out a lil, for example if some1 was talking and a bomb explodes i would have a hard time hearing the talk. that i think has alot 2 do with the fact that i was running 4 monito 70 tower speakers and my center was a harman kardon satellite.

i have narrowed my choices down to 2 speakers. i have enough money to get 1 speaker so money is not a issue and as i stated b4 i dont have a center right now and have to get 1. plz help me pick 1, which 1 is louder and more powerful? which 1 will compliment my towers better?

polk CSIA4
AND
polk CS20.

CSIA4 LINK: http://www.futureshop.ca/catalog/proddetail.asp?logon=&langid=EN&sku_id=0665000FS10090938&catid=

CS20 LINK: http://www.polkaudio.com/homeaudio/tsi/specs.php#center

my current system is as follows:
1 X HARMAN KARDON AVR 354 (not in pics)
1 x VELODYNE DLS-5000R 15" SUBWOOFER
4 x POLK MONITOR 70 TOWER
1 x missing
2 x POLK RTI4 BOOK’S

pics of my HT:
http://s719.photobucket.com/albums/ww196/unatiq/?albumview=grid

CS20 is louder.