can a new amp amp tame my speakers?

I did read your earlier posts, and somehow missed the part of high volume causing problems with the highs. I've just reread it, and sure enough its there. Another amp, perhaps with more power might help, then again it might not. Are the added subs self powered?

I'm of the opinion that one should purchase an amp that best allows the speakers to do all that they're capable of, not fix the speakers.

That your powered subs didn't seem to help alleviate the high end issues, makes me wonder if the problem isn't just inherent in the speakers themselves. Does the problem occur on all or just some recordings when the volume is raised?

Just a thought:
http://app.audiogon.com/listings/solid-state-conrad-johnson-evolution-2000-2013-02-12-amplifiers-19464

I haven't actually heard the combination, in fact I'm not sure that the Kappa's I heard so long ago where the same as yours.
I do seem to remember that back in the day the Infinity IRS' (along with the Wilson Wamms) were the top of the line, most expensive speakers going. I could be wrong, but I think those IRS' might have used something like the emits that are on your Kappas. This is a long time ago, but I seem to remember that tubes were the only way to go with the IRS' (the bass panels had their own ss "servo" amps built in), and c-j tubes were a popular choice for them, but even with tube amps, some used to cover the IRS' tweeters with tissue paper to attenuate the brightness. In as much as that might seem to be an anathema on a speakers that cost around 50-60$K in the late 1980's, it was pretty effective. I even have a friend that uses the same fix today on some old Linn speakers.
Those IRS' midrange/tweeters did some magical things, and are still sought after today, but obviously they weren't perfect (at least IMHO).
I believe your speakers have a nominal impedance of about 6 Ohms, but I have no idea what the minimal impedance is. The use of self powered subs might be very advantageous with them, but that's purely speculative on my part.
As well as I can remember (not very well), I remember the Kappas as being OK, but found other alternatives preferable. You might very well disagree.
The c-j I hyperlinked is actually a tube/ss hybrid, seemed like a calculated safe choice. YMMV.

Have you heard any other speakers besides the PSB's? Perhaps something like the Vandersteens 2's? The cost of which would be significantly lower, low enough to buy a really good matching amp too, for the same price as the PSB's. The used market has some steals too.

As I started on this thread, I suggest making sure want to keep the speakers you have, before doing anything else. If you do fine, by all means get the most out of them within your means.
If your not sure, or plan to change the speakers down the road, stop, you'll be going down a road that is likely to be marred with unnecessary obstacles, effort and frustration.
As far as making suggestions that also cater to some visual considerations, well, that's where I take the nearest exit.
Good luck, I hope you find what your looking for.

Was the "dome midrange" broken?

I tend to agree with Audiolabyrinth. Some how Krell has gotten an underserved reputation for being bright (at least IMHO), at the very worst they can be perhaps a bit grainy in the treble, but not bright. If anything Krells might be a touch dark. Krells usually have lots of power and amazing dynamics, both micro and macro, which may or may not explain this unfair (IMHO) reputation. Or could be that they've been victimized by their own success?
I also find that their intergrateds don't have the same composure that their separates do when asked to work 4 Ohms and below. YMMV.

Sometimes ones dissatisfaction is in the recordings themselves and not necessarily with the playback system.