Thinking of adding a sub---maybe not?


Looking for some advice. I'm thinking of adding a sub to my system and the one I'm considering is the REL T7. I've had subs (Canton) in the past with my older systems but it's been many years since then. My system today consists of a Luxman 505UXii integrated amp, a Marantz ND 8006 CDP/streamer, Dynaudio S40s and a pair of Tekton Lore Reference--I alternate the S40s and Lores through speaker A/B on the Luxman. My room is about 16 x 25. I love my system but after having subs in the past and getting the bass 'punch' from the subs, I'm debating whether I should go that route again. I've tried the loudness button on the Luxman but it just doesn't give the same results as a sub would IMO. Thanks in advance. 
bluorion
@mwinkc Thanks for the input--I've tried adjusting the tone controls but just I wasn't too happy with it. Hence, thinking of the sub. I realize my room acoustics is playing a part with this too. So a tweak here and a tweak there has affected the sound---some good and some not so good. I'd like to at least try a sub from a dealer with a return policy just in case. Great suggestions on here btw---thanks again!
That's a big room.  I'd add the subs, but suggest keeping the gain way down so it's barely noticeable, and using the lowest low pass frequency setting.  I suspect the biggest mistakes people make with subs is trying feature them, rather than just letting them augment the bottom octave.
One of my better decisions was adding a small sub (Rel T/5i) to augment a pair of Kef LS50 standmounts. It significantly increased the soundstage width and depth and provided some needed body to the music. The little Kefs don't sound so small anymore.  
I own PSB Stratus golds and added 2 sunfire hrs12's with them . I was astounded by the sound improvement.