Thanks everyone.
I'm thinking of going as high as $2000 and I'm leaning towards the Rotel RSX-1550 or the Sony STR-DA5400ES, which WHAT HI*FI? SOUND AND VISION magazine claims is better for the money.
Since we're talking an increase in budget, do you have any further thoughts for a receiver?
What I would do is find a receiver that had preamp outputs for all channels and had all of the features I wanted, from a reputable company (e.g., Yamaha, Denon, Marantz, Pioneer, whatever). If the Yamaha RX-V667 had all the features I wanted, I would not pay more. I would try it out with the speakers, and if it could not play the speakers as loud as I wanted, I would then buy a separate power amplifier. Generally speaking, putting extra money into a receiver is like flushing it down the toilet. This is because you are unlikely to hear a difference in most cases (if they are set up properly), and because it is the part that you will most likely want to upgrade in your sound system when they come out with new features.
The reviews of your speakers suggest that the impedance dips are not a major issue, and so I would not be overly concerned about it. But if whatever receiver you buy seems to run hotter than usual (which can be hard to tell, as many of them run pretty hot), or if it actually shuts down (goes into protection mode) when playing loud, or if when playing loud the sound is distorted (which, however, could be caused either by reaching the limits of the speakers or the amplifier), then I would be looking at a separate power amplifier. And a separate power amplifier can get you more power than you can get in a receiver, so this will likely be the better way to get more power anyway.