Curious - "An amp and surrounds will be added later."
Amp??? The Denon is an AV Receiver?
It looks to me like you are missing Center and Surround.
I have to say, I love a bargain. My motto is never pay retail.
I would say you are on your way to a fantastic system. In fact, I would say you already have a fantastic system.
When you bought the CM9, whether you like it or not, you committed yourself to buying the CM Center speakers, of which there are two
B&W CM Centre 2-S2, which I expect to be expensive -
The Midrange driver on the Center is a real advantage as it lowers the crossover on the bass speakers, and reduced lobing.
However, realistically, the standard 2-way B&W CM Center S2 would still do a fantastic job of it.
The standard price on the CM Center 2-S2 is a very considerable $1250 each.
The price on the cheaper CM Center S2 is a more modest $699 each.
These are for the CM-S2, the latest series. The last time I was in Best Buy the offered me a deal on the previous NOT-S2 models which are still very good. You might be able to get a deal on either of the older Center speakers, but likely only while stock lasts.
Surround are a little more flexible. You don't want them grossly different tonally than the front speakers, but in general, you can skimp here a bit. Typically people will do this when room circumstance force them to. But the surrounds are less critical and can be adapted to your need and budget.
That should be a fantastic system even as it stands now.