No, the SX-1250 is not too much for the Kappa 7s. In fact, it is the reverse: the Kappas are too much for the SX-1250. Or more accurately, they are too little...
To clarify: the Kappa 7 speakers belong to a category of speaker commonly called "amp killers". These speakers will, when driven hard, dip down to 1-2 ohms impedance. That is what I mean by "too little". Most amplifiers will work themselves nearly to death trying to "feed" enough current to satisfy the demands of these speakers.
You might make an analogy with someone trying to blow through a straw; almost anyone can blow through a thin straw, which offers a small channel with stiff resistance, but it takes a lot more lung power to keep blowing the same speed of air --and thus, a large volume of air (analogous to current) through a large, fat straw with low resistance (equivalent to low impedance here). It takes real "lung power" --i.e., a high-current-capable amp-- to handle such demands.
Please understand that a high-current capable amplifier is not the same thing as a speaker with high wattage output. Your SX-1250 is powerful, in the sense of putting out a lot of watts, but it is not capable of handling the demands of the Kappa speakers, especially if you turn the volume up. It just wasn't designed for it. Match it with a speaker that presents it with an impedance of say, 8 ohms or 6 ohms, and it will sing happily all day at high volumes. But let the impedance drop to 3, 2 or even 1 ohm, as can happen with old "amp killer" infinities, and that SX-1250 will be struggling to keep up, like a tired, drowning man in deep water.
When pushed to higher volumes, the power needed to move the woofers (against the air compressed in the sealed boxes) is substantial. In trying to keep up with these demands, the speaker resorts to "clipping", or chopping off the tops and bottoms of the characteristic waves. If you were to look at the output on an oscilloscope, you could clearly see the flattened "chopped off" wave tops, but you can't always hear this when it is beginning to happen. [With practice, you can learn to recognize it when it gets significant, but why do this, and risk your gear just to learn something you shouldn't hear, which you can avoid/prevent?] This clipping action puts severe demands on the tweeters, and soon "fries" them dead! It may also damage your amplifier (receiver).
Get a HIGH-CURRENT CAPABLE amp that can safely drive loads in the 1-2 amp range, and you can run those Kappas as loudly as you like, without worry. There are many such amps out there, including some models from Adcom, Krell, Soundcraftsmen, Ampzilla, and others...
But if you keep trying to drive those speakers with your receiver, you'll end up replacing many more tweeters (rare and costly, since they are no longer produced), and eventually ruin your receiver, too.
DO NOT try to pair up these units; it is like trying to use a volkswagon to pull an interstate trailer rig; just not an appropriate match, and such a mismatch will inevitably lead to catastrophe. If you MUST do so, ONLY play them at very low volume levels, but even that I wouldn't recommend, as the temptation to push it "just a little bit louder" until it is too much, is probably too great.
Get a different, more appropriate pair of speakers for your receiver.
Get a different, more appropriate amp for your speakers.
If you MUST have the 1250 sound through the 7's, then take the pre-out signal from the 1250, and run it through a power amp that can safely handle the 7s. That will give you the best of both.
Do some searches around here using words like "amp killers", "high current", etc... and you'll find a lot of information on this topic. Learn the easy way by reading up, and protect your gear. Otherwise, it's a certainty that you will learn the hard and costly way.
Incidentally, you have some GREAT quality gear with those two models. I have both, and like them both very much, as do many other happy owners around here! :yes:
:thmbsp:
Good luck! :thmbsp:
Usually, though, I used the G9K for the upper end and a Denon POA 2400A for the bottom end. It's pretty easy to overdrive an amp into AR9s, but you're right, about the only thing that happens is a dead tweeter.