It depends on a couple of things...

First, do you have 7 channels of speakers? If you do, then you will be using all 7 channels of the 7100 for speaker duty (left front, right front, center, right surround, left surround, rear left surround, rear right surround). If this is the case, then you will need another external amplifier to power your sub.

If you don't have seven channels of speakers, you can always feed a channel of the 7100 with the subwoofer output from the 950. Remember, the 7100 is basically just 7 channels of amplification in one box. The channel input labels on the back are just a helpful guide put there by Outlaw. Those channels will only amplify what you tell them to!

Most people will tell you to get more than 100 watts for a subwoofer, however. In this case, you have still have options. You can buy a M200 or similiar monoblock amp and use that to power your subwoofer. Parts Express sells monoblock subwoofer amps starting at around $80. What's nice about a seperate subwoofer amp like this is that most include some sort of phase switch and also their own built-in crossover which can be helpful in setting up your system. I personally use a PE subwoofer amp and it works just fine with my set-up.

So to answer your question; It depends on how you set it up but it is possible. Good luck!