Oh, absolutely (and hardly a new thing). It's the same with the 900 W claim — that's the total power going to all speakers, not the power to each channel. I'm mildly curious about which speakers are what. I think the 6x9s are just woofers, which would imply that the smaller drivers are all two-ways (mid-range/tweeter).
I can't say for certain on other models, but on the HK, the 6x9s are in fact just woofers. The frequency cut off is at about 1500-2000 hz. Nothing above that goes to the 6x9. There's really no point in installing a 2way 6x9 unless of course you run it from a different amp.
I'm pretty sure the 900w claim is also peak watts, not RMS. RMS is often 1/2 of peak or less. That price RMS at 450 and that includes the sub. Assume 150w goes to the Sub then you're left with 300w to the remaining speakers. This equates to 20-40w per speaker if all receive power evenly. And that's probably generous because we have no idea what the true RMS numbers are.
That all said, the factory amplification system for these is more than adequate for most people. For those who want more, you'll have to go down a pretty deep rabbit hole.