Floor Stander or Monitor w/ 2 subs? What does the later give up in a large room?

My listening room is also the Living room. My wife would love to get rid of the floor standing Silverlines. I can deal with that since I've had these for a long time. Change is good. But will it be a good move to go to monitors with 2 S-5 Rel type subs? I am considering Watkins Gen 4 speakers. I've heard them and they sound very good. But will they fill a 5000+ cu ft room?. That is my only reservation...size of imaging. What else...or am I wrong in my thinking they will lack anything? I will try them but I'd like to know what to look out 

Thanks