I do own a HT-S9100 THX which is the "grandfather" of the 9400. The only difference is the amplifier which is upgraded by Onkyo within each new generation. In the 9100, the amps was in a way similair to the Onkyo 606. I guess now they have something that, feature wise, is similar to a 608. Except that, the speakers are the same.
Back to my case. My living room is 18ft x 12ft and the set does its job nicely. The sound fills the room and the bass is more than adequate (at least to my neighbours taste).
I could get the system at a reasonable price (700€ instead of 990€: don't forget that EU prices are usualy higher the US ones).
I'd say if yoy can get it at a good price it's a good start point. You could easily upgrade the speakers later.
Now, some say that within the 800$-1000$ range you could pick the same amps (608,...) and get separate speakers with better reputation (and sound). It's now really up to you and depends on the price you can grab it..... Also, if you want to avoid the hassle of choosing separates elements and so, this kit might fit the bill.
Oh yeah, before I forgot. The wires provided suck. Take into account that you'd better off upgrading them right away....