Pass X150.5 vs. X250.5

I agree that you should look at the room. IME, some adverse room effects, particularly in the high frequencies, are inaudible at lower volumes, but quite noticeable at louder volumes or during peaks.

Here is a 10 second test: Standing in a couple different places in the room, clap your hands loudly. What does the decay sound like? Is there ringing? You may have a flutter echo that is bothersome only on peaks.

If you do have a room problem, then adding diffusion at this point may be a better idea than adding more absorption, but both should have a significant impact.

Bryon

Bryon is right IME. Try diffusion on the back wall versus absorption.

Ceiling though is a nice area to address as it too is a first reflection point. But ceilings are a bit more difficult from an aesthetix stand point.

Ccanino,
Adding to the room treatment remarks made by Bryan and Ckoffend, I might suggest you temporarilly take your side wall 1st reflection absorbers and move them to your back wall (behind the listening position); reflections from the back and front wall are more troublesome than side walls and ceiling due to the lower angles of incidence which reduces apparent source width and spaciousness.

Diffusion - either 1D or 2D - on your back wall works well depending on your sitting distance. Note that the diffusion coefficient depends on the angle of incidence of sound, with the greatest diffusion occurring at 0 degrees incidence, and because of the lower angles of incidence from your speakers to the back wall, diffusion can be very effective in helping to add "listener envelopment," a positive thing.

Many people mistakenly walk in a room, clap their hands and hear slap echoes not realizing it does not accurately represent what they hear from the loudspeakers when sitting down in their chairs. Slap/flutter echos will be most audible with short transient sounds - and probably inaudible with sustained music. Be sure to have someone stand next to or over your speaker and clap their hands while you listen from your listening chair to detect whether flutter echos can be heard there or not.

Good luck and keep us posted.

You might also look into your AC power. Is your Amp plugged into a dedicated line?

Update to the problem. As hard as it is to believe, I changed the power going to my pre-amp from a conditioner that had my digital front end plugged into it to one that only had an analog device plugged into it and the harshness was almost completely eliminated. This even though the MFR said the outlets were isolated. Then tried heavy curtains on part of back wall, but that made things too dull, so guess I'll live with the considerable improvement the conditioner switch gave me, until I can get some diffusion for the back wall and try that. Thanks to all! And keep the ideas coming.