Taken from a thread on another forum- my experience and continued enjoyment with a pair of REL t9i subwoofers in a room of similar size to yours-
"REL T9is are tuned and ready to review.
Let me start by mentioning my experiences as they relate to common thoughts about REL subwoofers (myths vs. reality) as they apply to these T9is in my room and system.
Common thoughts-
REL subwoofers cannot play deep. MYTH. These T9is are measuring flat to 20Hz at the listening spot and play deep and sustained quite well.
REL subs are musical, fast and have good tonal definition, low distortion and emphasize quality- REALTY. So far I have heard many shades of bass and the notes are well presented and represented with dexterity. Zero bloating, bleeding and sluggishness.
REL subwoofers are easy to setup and integrate because of their quickness. MYTH. If you really care and pay attention to the sound, they are no easier to integrate than any other subwoofer. Proper technique and process are still required- however they are quite "integratable" even without variable phase control.
REL subwoofers are not punchy. MYTH! These t9is are punchy as heck !
REL subwoofers are a poor value. Leaning to MYTH. So far they sound better than any other subwoofers I have heard or owned and are a perfect compliment to my system. Previous subs include JL Audio D110 and Martin Logan Dynamo 800X. The RELs beat each of them easily. It seems like you get what you pay for. Note- I have heard but not owned SVS subwoofers so I cannot comment on their value. Right now I have no interest in them based on the sound I am hearing which is excellent.
Final comments- they do not harm the midrange! The clarity and transparency I have without subwoofers is still there with the subs engaged and tuned properly. Unlike previous subs I have owned.
I love the sound and they are keepers".