Given the 2.9's are like most NHT's and very inefficient I would seperate the amplification of the 2.9's especially since you will already have the amplification. Use the 7100 to amplify the top of the 2.9's and the Hafler for the bottoms. Since the Hafler has it's own gain control (unlike the 7100) you can dial in the sub section of the 2.9's a little better. Overall I think the 7100's 100 watts is a bit shy for the 2.9's while driving them full range.
Since you are going for a HT setup, the need for a center speaker is critical IMO, and I would go with a matching center like the AC-2 or even the AC-1. Matching the rears is not quite a critical so the Zeros would work just fine. I read you want limit additional purchases at this time but it seems that with the addition of a center channel you would have all you need at this time for a pretty nice HT setup.