Well if I'm reading the info correct for both the 6 and the 7 the bass extension is down to 36Hz and 35Hz respectively. That's pretty good for music but isn't really going to shake the house in movies. Now how much punch they have behind them I don't know I've never heard them. I can tell you that my Paradigm Monitor 11's with 3 6.5" woofers, 1 6.5" mid, and a 1" tweeter will shake my house with my 100W Rotel without breaking a sweat.
Now one thing that I'm seeing just taking a quick look through the manual for the 254 is that there's no power ratings for anything but 8ohm speakers. The Dali's that you are looking at are both 6ohm speakers. Now this might not be a problem but it is going to put a little more stress on the receiver, is the H/K even rated for 6ohm speakers? If you only have so much money I don't want you to buy something and then blow it up, maybe someone else can chime in with more experience? There are plenty of receivers out there rated for 6ohm speakers so if the H/K can't do it there are more options. Stick with the speakers you like and find equipment to go with them, have you listened to the Ikons?
I know that put a lot more questions out there than answers I just don't want you to waste any hard earned money, I know I hate doing that.
I can't tell you how many times I've commented on this. Perhaps I should just write some articles and post them on the internet.
Under normal home use, you can ignore amplifier impedance ratings. While they are meaningful at or near maximum power output, home use doesn't get amplifiers anywhere near their maximum power output. In systems with powered subwoofers, it is hard to get a receiver amplifier above a handful of watts of output power. My own 130 watt per channel receiver hasn't yet gotten above 20 watts per channel during loud peaks in movie sound tracks. Average output levels are just under 1 watt per channel in my listening room. I choose a volume level that puts dialog at the same level I would hear if the actors were in the same room with me. That isn't going to burn up speakers of any reasonable nominal impedance measurment. Nor is it going to cause an amplifier to fail.
Speaker impedance is not constant. It varies over the range of audible (and inaudible) frequencies. Impedance ratings are called "nominal" which you can view as average. The difference between 8 ohms nominal and 6 ohms nominal is meaningless in a home theater except under the most extreme circumstances.
Since it is possible to break things at or near maximum power levels, it is sensible for manufacturers to want you to use the highest impedance level possible. The reason is that, under abusive conditions, the unit driving a lower impedance load would fail before one driving a higher impedance load. They could publish a 4 ohm rating and a 2 ohm rating if they wanted to. But those ratings would come with significantly lower power ratings as well since most receivers aren't designed with high current output stages. People don't buy low power ratings. They have been trained by the industry to want more and more power. In other words, because the manufacturer chooses not to publish 6 ohm specifications does not mean the product can't handle 6 ohm nominal impedances. In fact, it can do so with ease.
Incidentally, one of the Audioholics people posted an interesting article in the speaker forum in which he burned up some speaker drivers purposely in a test. You can get an idea of what abusive use means in that article. It is pretty interesting.
This equipment is not designed to burn up. Think of how nonsensical it would be to design a unit that was sold to the public that would destroy itself with the first movie it encountered. The public is not made up primarily of engineers and electronics experts. Most of them don't even know what impedance means. Buy whatever suits your fancy, relax and enjoy the audio.
