Are you sure your room isn't causing the problem? 15dB of boost below 20Hz seems a bit excessive.
If you do go with the DO LMS-R you will be gaining cone area while losing a bit of xmax (25.4mm vs 28mm). The voice coil on the LMS-R is vented through the rear of the magnet so you do need some clearance for that. I don't know how close you can put them together, but I would feel comfortable with 2" between them.
JVC DLA-RS45U projector - Seymour H115 screen - Samsung UN65EH6000 TV
Fusion 12 Tempest L/C/R - diy coaxial surrounds - SI HT18 subs x4,
Denon AVR-X4000 - EP4000 x2 - Minidsp
HTPC w/AMD R9 270X - Linux Mediaserver w/ 18TB storage - PS3