Hello FordPrefect,
No, there are no plans to replace the hybrid tweeter on the QS4s. It's a matter of having two distinct QS surround models, one for medium to small rooms, the other for larger rooms. The voice coil on the QS8s is 1 inch, compared to a 1/2-inch voice coil on the QS4 tweeters, so it's just a matter of improved power handling at high volumes in bigger rooms.
The actual frequency response differences between the two tweeters would be insignificant. The same applies to the larger woofers on the QS8s vs the smaller ones on the QS4s, but the QS8s pump more air into bigger rooms with lowered distortion. They are two different models for different applications at different prices.
By the way, as you get older, you do lose extreme high-frequency hearing but the good news is that it doesn't matter--there's little musical content of importance between 12 kHz and 20 kHz. Although audiophiles cringe when I tell them this, all of the important energy and content of most instruments lies in the midrange and upper mids, to about 10 kHz. That's why a speaker's performance through the midrange is crucial. It's also where our hearing is by far the most sensitive, and where we largely make judgments on good or bad qualitites of speaker performance. So don't worry about a few harmonics of cymbals or violin at 18 kHz. You'll never miss 'em. Besides, most males over 40 have little or no hearing left above 14 kHz, no matter what they claim.
Regards,
