I don't believe any movies are in 7.1 yet so the 5.1 is a good choice...I would have preferred the 5.1 and 200W but am in a similar boat to you...I replaced everything in one fell swoop so...I got the 7100...
I bought the 950/7100/LFM-1 combo and it is great...I have only had it a month and the speakers arrived later so not many movies but it sounded very good with Blackhawk Down and Band of Brothers...plenty of action and explosions...in fact a German Rocket that went over my head sorta scared the %$^&* outta me, so I guess that means it works!
Actually, I think 100W is PLENTY and 7.1 for the future...if you pick up a 755 that's great too...the Outlaws service is great and this place is VERY helpful!
I hope this helped...the REAL techies will respond to you soon enough
Bill