I have a 7125 and a 7500 amp and there is no discernible difference in the sound quality between the two. The XLR connections allow for longer runs of cable without interference and they provide about 3 db more headroom for difficult to drive speakers. The 7125 is very similar design to the 7200 and I would keep the system as is if you are happy with the sound right now. Plus as stated above you have two extra channels to use as needed.
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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