I recently bought 2 pair of Valencia's, which look identical on the outside. They have a different crossover and wire hookup on the back, and different speakers. The one pair that said on the panel Altec 846B, both had the horn drivers blown, and one had a blown capacitor. I replaced both the caps in their crossovers, and bought new diaphragms from Simply Speakers, number 26420xx, which were supposed to be Altec and not imports. I found out later that GPA would re-magnetize and replace the diaphragms for a little less than I paid for just parts. Oh well.
The other pair I think might be Heathkits, with Altec speakers. I noticed as soon as I hooked them up, that these guys really sound like a live performance. I am a novice at most of the terms used by audiophiles, but I did hear what sound stage is all about. These speakers are night and day different than my KLH 915's which also have a 15" woofer. They open up the room, and drums sound like they are right in front of you.
However, on certain songs, they have a shrill sound that hurts your ears. Jethro Tull Aqualung for example, when Ian is singing through the megaphone, it is very shrill on all 4 speakers, but more so on the Heathkits.
The real Altec have a 806-8A horn, the woofer says 50 03 030767, and the crossover says N800-8K network. They had the blown cap in one, and I replaced both caps in both of them from Parts Express.
The other pair, which I assume are Heathkits have the horn an Altec 806A, and woofer says 803B. They both also say they are 16 Ohms, instead of 8 like the other pair.

My Questions:
1, What causes the shrillness? Is it the crossover, or jus the sound of the horn? My 2 types of horns look identical in their aluminum construction, except one pair is black and the other a blue. Could putting spray on foam on the outside of the horn stop some of the shrillness?
2. I have read that capacitors that are 35 yrs old deteriorate. The crossover in the Heathkits don't have the caps accessible, they are all layered in like a black rubber, inside a metal box, where the real Altecs crossover was like a circuit board with the caps plainly exposed.
3. They both have an adjustment knob on the outside, which I have set at 0, the highest treble setting. Can getting rid of that help the sound, by taking something else out of the circuit? Turning it to anything else takes the cymbels out.
4. I have also read about Behringer external crossovers, and about passive and active. I would assume the Behringer is active, and what I have is passive. They have one for about $90. Does it do both channels, or just one? Do I have to run 2 wires to each speaker, one for the woofer and one for the horn to use something like that?
5. What does the 16 ohm relate to in real sound? All the amps I have seen say they support 4 or 6 ohm, and some say 2. None say 16 ohm.

Any other suggestions? I have a Harman Kardon AVR 635 7.1 amp, but am running preamps signals now into 3 different 2 channel 500W power amps, as the HK would turn itself off on loud volumes. I think I have plenty of undistorted Watts, and the shrillness only happens when I crank it. I have spent several hundred $ so far on components, cables and such that didn't make an audible difference. Can someone here lead me in the right direction?