Check out Aperion. They have free shipping and a 30 day in home tryout deal. The speakers are first rate construction and finish and get very good reviews as HT systems. I have one of their subs and am very happy with it.

If the Missions are in decent shape, why not upgrade the center and add the Outlaw sub and see where it takes you. Whatever you decide, try to get speakers with similar efficiencies especially across the front LCR
_________________________
Music system
Model 990/7500/Magnepan 1.6 QRs/Technics SL1200 MK2/Aperion S-12 Subwoofer/OWA3/Sony NS75H DVD
APC H15 Power Conditioner

TV System
Large Advent Loudspeakers/ Polk center/Monoprice surrounds/Panasonic Viera 42 inch/Onkyo HT-RC260/Sony BDP S590/Directv


Home Theater System
Onkyo PR-SC886/Outlaw 7125 Klipsch RF-82 L/R,RC-62 center, RB-35 SR/SL, BENQ HT1075, Outlaw LFM1-EX/OPPO BDP-83/Directv
Harmony ONE
Blue Jeans and Monoprice interconnects
APC H15 Power Conditioner