Yea this is my theory. (I could be wrong). It even seems it can deliver the output I want for a very short period of time. Before it starts. I have backed out as soon as I hear it’s beginning.
Is there a way to tell for sure what’s going on?
It's good practice to turn it down immediately if you hear audible changes. Audible changes means you're already way outside SOA, and rapidly approaching "let out the magic smoke" territory. Don't break your stuff (hopefully you haven't already). You have to reel in your "loud as a concert" expectations.
So, is it the speakers? Follow everettT's suggestion about crossover settings. That will reduce cone motion (protecting the speakers) and get a tiny bit more dynamic range, while ever so slightly easing the load on your amp. Now both of those benefits are marginal at best, so don't get your hopes up. A side bonus, it probably will be easier to blend the sub at 80hz, by virtue of sidestepping phase shift issues of the Klipsch down at 40 hz.
-Your amp still may not have the requisite power for your desired listening habits. The speakers could withstand a more powerful amp, one that's not clipping when you're blasting it.
Is it the amp? Based on what you've told us, likely so. Despite your speakers still fairly high, if exaggerated sensitivity, you must consider that power demands go up exponentially, while your Denon is only modestly powerful.
Guestimating via
this callculator (I used 89db/w/m sensitivity, as your speakers real sensitivity is 92, the calculator is based on watts not volts, your speakers are 4 ohm, so minus another 3 db; 2 speakers; 12' distance, a total guess), and at the redline (60 watts...which could be optimistic if powering a full surround system) your amp can do about 98db, peak.
So lets say you could do average 89db with 10db headroom for peaks, which is enough for rock. That's reasonably loud, but not concert loud. If you crank the volume way up to attempt to get it concert loud, you're clipping the amp. If your program requires more than 10db headroom, your average levels will be forced even lower. Like previously mentioned, your expectations may have to be adjusted downward.