High Level Distortion

I'm hearing significant high level distortion in my system, so I thought I'd post here.I'm wondering if it's the Marsh A400
Equipment: Marsh A400 and Antique Sound Lab Hurricane amps, First Sound Presence Deluxe Mk. III, Arcam FMJ 23 CD player, Nordost Valhalla and Valkyrja interconnects, Shunyata Andromeda speaker cable and power cords, Sound Dynamic RTS-3 and Hale Rev 3s.PS Audio Power Plant 300 and power cords, Nordost Pulsar points, and Walker Audio resonance devices.
The room is acoustically treated with ASC Tube Traps and ASC sound panels. The amp, preamp and PS Audio are all on their own circuits (20 amp, just installed in new room of the house).
The most noticeable and obvious problem is how the soundstage congests during high level passages, around 88db. It tends towards harshness, too. However, when many instruments play at once, some of the musical lines disappear, too (this phenomenon is not new, just mentioning it).
I'm wondering if it's the Shunyata Andromeda speaker cables, but I substituted some older Monster M1 speaker cables (circa 1998)and the effect remains.Besides, the Shunyata review on Soundstage would indicate this is not a trait of the cables. Still, I need to investigate everything.
I should point out that the Antique Sound Lab Hurricanes do not exhibit this effect in the system, although I have not yet tried them out in this particular room (blew a fuse in one amp, which is being replaced).
I cannot tell if it's the CD player, the amp or a speaker/speaker cable interaction.
Any thoughts?