Likely culprit for harshness at higher volumes?

My best guess is it is the CD player and maybe amp. I doubt it is the speakers or room. Higher order harmonics are not genrrated by the room. You can take steps to improve room acoustics, but that is more like icing on the cake and no way to fix bad equipment. When i first started with CD, my first impresion on 90% of CDs was things were way too harsh at even moderate volume levels . I found the only real way to improve things was to get CD players with way better digital filters and analog stages. I made the natural progerssion with better players and noticed a big improvement with each step. I went from Pioneer BPC, to Theta, to Krell, to Wadia, and back to Krell. :)
you might look for any reviews on your amp to see how it does higher order harmonic distortion. I know Adcom only really made one amp that was even close to "high end", that being the model designed by Nelson Pass. The rest of Adcom amps are strongly mid-fi and not much more than BPC. (sorry to say)

Hi -- thanks for continuing to check in on this topic and offering your suggestions. I am continuing to experiment, mostly with fabric (types and locations) for reflections, speaker location (separation and proximity), analog vs digital interconnections and various types of music (classical, jazz, vocal; low (ie - bass, sax), mid (vocals / guitar) and high (some vocal and violin) pitch sounds across various volume ranges.

I've been spending a lot of time listening, moving stuff around (including using a different room and moving components between rooms) and characterizing. :) This seems really more of an art than a science.

I've tried a lot of things and I think I'm reaching the limit of room dynamics and my components without buying stuff (dampeners, drapes, different components, etc).

While it's not perfect and some harshness is still there, it's definitely better than a few days ago and I'm actually able to turn up the volume quite a bit more before the harshness becomes unbearable. Again, before, I would get unbearable harshness before the sound was uncomfortably loud. Now, I can get the sound to be uncomfortably loud before the harshness is really unsettling (and perhaps I'm also now reaching the limits of my speakers and/or amp). The clapping / pinging test is much better now, especially in corners where it was the worst.

I appreciate the suggestions and understand the reasoning for a power conditioner and the headphones (actually, I really want to buy some nice headphones and using them for additional testing here is an additional reason). And I keep learning new things: I had to look up the Fletcher-Munson Effect (never heard of it before). BTW, what is BPC (as in, my Adcom amp are not much more than BPC)? Not that I disagree but just not sure what it stands for. :) I think my GFA-5400 is rev 1 of 2 versions (I have the rev made in Japan, not China).

But, given my budget, I can almost buy a used CD player that may help improve a weak link in my system (access to additional bits and higher sampling rates); I think my current DACs (in both my AVM2 and X111ES are 8 or 16 bit and 48 or 96 KHz). Perhaps getting something like a used Cambridge Audio CD player in the $200 price range would be the best use of any budget I might have.

Or maybe I should just be happy with what I have. It doesn't actually sound too bad now after trying some of the inexpensive suggestions received; it's not perfect but better. But I can see how a budget could very quickly spin wildly out of control here. :)

Your Adcom is having difficulty with transients. The poorer the recording, the more apparent this becomes. Try a really good one like say, Lyle lovett's "Natural Forces" or Jimmy Roger's "Allstars", or Ray Charles' "Genius Loves Company". A really good amp won't be limited by the recording in that it will simply reproduce what's there accurately. So if the information is diminished, it won't attenuate that upper mid-range already attenuated in the poor recording we're all familiar with as "harshness". The recording will simply be apparently "lacking". If a great recording eliminates the issue, you need to consider the perfomance of your amp. All KEFs are great speakers regardless of there particular shortcomings. If it hurts or is bothering you that much, it's the amp.

@Csontos: Thanks for the suggestion. I want to make sure I understand the methodology. The presumption is that a well recorded CD (ie - something that is well mastered using larger word sizes (24bit?) and higher sampling rates (ie - 96 or 192KHz?) and well done (ie - good recording studio, good equipment, etc) should play well on any system (up to the limits of said system).

The assumption here is that the pre-amp and speakers are not the weak link at the volumes I'm using. And even a source that is 8 or 16 bit at 48 or 96 KHz should be sufficient for a good recording to highlight deficiencies in an amp.

So, by playing a known good recording (like ones suggested), I can determine if the amp is limiting if there is harshness detected.

Whereas, if harshness isn't detected, then it's just poor recordings I'm listening to (in addition to other things like room acoustics)?

Actually, I've been wondering if there is a way to challenge each component in some way. But I've just learned that this way of thinking may not be useful -- that components play off each others strengths and weaknesses so you need to measure the system as whole in the room you are targeting. Must drive audio component retailers crazy - a component that sounds good in the store may sound lacking at home :)

So, if I learn that the Adcom is lacking, I guess that's what the amp forum is for. :)

That's just it. It's not the good one that reveals the amp's true potential nearly as much as the poor one. The amp is the heart of the system. Once you've gotten used to the attributes of your other gear, you then begin listening to, guess what?... your amp, "again". The component you get used to the quickest is believe it or not actually the weakest link, your speakers. What you will never get used to are the shortcomings of your amp because they are constantly being revealed and so become your focus. For the amp to "disappear", it needs 3 attributes relative to your ears; it has to be "fast", it has to have a truly flat frequency response- one that is not can seriously contribute to the harshness you're talking about, and it must be very linear. Whatever other attributes it has are a bonus A truly high-end amp is probably the one that leaves you scratching your head wondering what makes it a high-end amp because it's so "flat and dry". Everyone out there building amps is applying their own brand of "voo-doo" in order to compete with each other. What I mean by that is it's easy to show a flat response on a 6 inch tape. Stretch it out 3 feet and you'll see just how flat it really is! It's not possible to add without subtracting, and they're all doing it fooling you into thinking you're getting a superior product. It's usually located in the bottom end and/or upper mid-range- it being the most bothersome since it thickens transients in the vocal range which can be fatiguing or downright ear-piercing. At first it's an up front in your face soundstage but then begins to take it's toll on your ears with lots of missing depth. Poor recordings should simply sound as they should.."lacking". They should not be ear-piercing or irritating at all! Remember, the entire system is nothing but a playback device. If the components are of sufficient quality and functioning properly, "revealing" poorly embedded information should sound as smooth and clear in terms of what's there, as the opposite. It doesn't "improve" it, but just plays it back.DC offset problems and bias issues can definitely cause the problem you are experiencing. Are both channels the same temperature within a couple of degrees? Have you checked the offset? These factors can ruin the sound of an otherwise great amp.