Added A Second Subwoofer To System

I haven't created a Virtual System yet so I will give a quick overview of my room and system.

I'm currently using a Classe CP-50 Preamp into Black Ice Audio Fusion 3502P power amp using the balanced in/out.

Speakers are Sonus Faber Lumina III's.

Subs are SVS SB2000 Pro and SVS SB1000 (not pro version)

Room is 13'L x12'W x 8' H

Subs went from both front corners of room to half way along both side walls.  

Listening position is approx. 7.5' from main speakers and 3' from rear wall.

I like the way the bass sounds with the subs in this position and although they appear close to my listening position, I can't hear or am aware of their locations.  

I set the phase for loudest output at these new locations.

My problem (?) is I feel that the overall volume of my system has dropped a bit.  I feel the need to turn the volume up a little louder than I did before the change.  

I'm actually concerned that I lost a little hearing overnight.  I am 63.  In all seriousness,  I doubt that I did although I know that hearing loss is inevitable.

Anyone experience anything similar?