Need help-new room advise

I just moved into a two story townhouse with a loft. I set up my rig(ARC LS7, Counterpoint transport, Sonicfrontiers sfd 1 mk2 dac, Anthem amp 1, old HK tuner). Anyway my problem is echo although it's not a lot but the clap test reveals some. I have wall hangings,corner tunes, but no back wall to speak of. There is a back wall but it's the upper part of the second floor and there are alot of windows. I plan to treat the windows shortly but would like any advise on keeping my music within the loft area as much as possible. I also thought of putting the other corner tunes on the back wall along with window treatments.( The back part of the loft has a banister/rail that I place my chair against).