You need to decide the key priority in your system. If (like me) you mainly use your kit for movies then the 3100s plus a 5500 sub would probably be the best utilisation of your budget.

If you heavily use multi-channel music then an all balanced 5200 set-up would probably be a better move. Of course if you change your preferences later you can always add a sub later. Your 5200 investment will not be in vain.

These are nice decisions to take. Do post your decision, it's good to see how fellow enthusiasts develop their systems.

Cinema: DSP750 x3, DSP3300 x 4, DSW.2 x 3, Trinnov A32, 271, Oppo 203, Toshiba HD-DVD, SKY Puck, Sony XW7000 PJ, Screen Research AT, Kaleidescape 4K 30TB
Lounge: 861v8, 808v6, UHD722, DSP8000SEPP, DSP7200HCSE, DSP3300, DSW x 2, 504, C15, Sony UBP-X800, SKY Puck
Bedroom: DSP5200SEHC, G65, UHD722, G08, DSW, M6, C15, 210, SKY Puck
Spare: 818v3