While this post is very old - there is always useful information to individuals searching for similar information.
The OPs post about congestion at higher volumes is not uncommon. In this case, I think the cause is one or more of several problems or issues:
1: The room can just become over saturated with snund. There is a limit that any room size can handle in terms of sound volume. Improving the accoustics of the room can address this, but it only increases the volume a room can handle.
2: The CD player, as the OP questioned can certainly be contributing to this problem (as can any component, but in this systems case, I think the cdp is a good starting point with equipment). I once owned a AA capitole that did not present this problem, but sent it in to be serviced and upgraded. Bought a AA Prima for interim use, thinking I would get 80% of the Capitole. The prima could not play large scale recording without becoming congested, more noticeable as volume increased. This went away with a better cdp.
3: Vibration control of components, speakers, et al. As sound volume and levels increase, everything in the room is subjected to more vibration and this notably start to break down the soundstage quickly. The Sophia come with spikes, yet many don't use them. Components don't typically come with good grounding/vibration devices (excepting some, ie. esoteric, etc. . .).
4: The Krell amp, while much less likely than the cdp could be a partial cause. The Showcase Series is by no means their best series; however, I am not saying this with any degree of certainty.
5: Power supply - dedicated lines, "proper" power conditioning, etc. . . can definately play a role. My concern here is that th OP reports this problem with only specific types of music. The same anomoly should occur with moderate scale but dynamic music as well if the problem is purely power quality related, IMO.
This same phenoma occurs at rock concerts when they have the gain turned up too high or the soun is just too loud. Contrary to what Spinal Tap says, 11 may not be better!
To find out how real the problem is in terms of the quality of the media, go out a buy a good Chesky records test CD that is known to be well recorded and should not fall apart or congest at high volumes. This will help id whether it is the recordings or the other causes.
As an FYI, this past week I had a $9300 preamp in my system that I was testing/considering. I encountered the same problem when I turned the volume up past my regular "loud" listening levels. I can't say whether it was my amps power (which I am in the process of replacing), my room or the preamp. Speakers were also Wilson (W/P in this case). I have owned Wilson speakers (5 pair) over the past few years. I know it wasn't the speakers from familiarity with use in prior equipment settings.
So in the end, one cannot answer such a question with 100% accuracy, but only point out the most likely scenarios which may require more than one step or change. Personally, my suggestion is to start with the cheapest corrections first - in this case the recording. Followed by the speaker placement/set-up. Listen in a nearfield environment and see if this addresses the problem (as it takes away much of the rooms interaction on what is heard). The go to vibration controls, then start replacing components or listen at slightly lower volumes?
