Distortion on piano recordings? Advice appreciated

I'm not sure exactly where to put this, but I guess amplification is as good a place as any.

For several months now I've been occasionally noticing distortion (fuzz) in my system, only on some piano recordings. It seems to happen when they get loudest, or when the note attacks seem most intense even if not that loud. It's only at mid-high frequencies (not lows or extreme highs). Seems to be the front channels only-- I plugged my surround speakers into the front channels and heard it then too.

In that time I've changed all my components (amp, processor, CD) except the speakers, and I have tested other pairs of speakers and interconnects with the same result, though it's perhaps less obvious with RCA ICs than with XLRs.

I'm pretty sure I've also swapped out speaker cables too, though not lately. I'll try different speaker cables again this weekend, but assuming it isn't them, could it be a room node? I don't know that much about nodes, but I thought they were usually problems at much lower frequencies. Can this be this severe in the higher ranges too?

Is there anything else I'm forgetting?

Halcro MC-70 Amp
Classe SSP-600 Pro
Hyperion HPS938 speakers
Aurum Cantus Leisure for surrounds
NAD M5/ Parasound players
Audioquest ICs and cables
I think it may be your amplifier 'clipping' as it runs out of power? The piano is one of the most dynamic of all musical instruments and the differences between ppp and fff are just about the greatest dynamic shift you can get in a recording.
You didn't seem to answer Drubin's question about it occurring at very low volume? If the distortion is still there at very low volumes, then it is NOT the amplifier clipping.
The Halcro outputs over 300 watts into 4 ohms. Your speakers are rated 90 db sensitive with a 6 ohm nominal and 3.8 ohm minimum impedance. Things look pretty good on the power amp/speaker side of things.

You might be overdriving the input to your Classe processor. Your statement that "perhaps less obvious with RCA ICs than with XLRs" supports this, since the balanced connections are 6db louder than the unbalanced. I note that the NAD has a maximum output of 4.2 volts balanced while the Classe maximum input rating is 3.6 volts.

Food for thought.
I also experience this with Fourplay's CD "Heartfelt" track no. 6. I often listen to music at moderate to high volume levels and got panicked when a few notes on the piano at a given passage got out of tune and distorted. I thought the speakers' drivers were blown or something but knew it was the recording as the defect remained when the the tune was played at low volume levels.

I would be glad if anybody who has this Fourplay "Heartfelt" CD can confirm on this. I suspect the recording engineer has screwed up on that particular part.

imho you have a broken or a couple of broken speaker drivers... I'd be curious to know what you find out eventually.

As members have noted, the piano is very dynamic and demanding and the problem will only reveal itself at particular frequences and intensities.

:) listening,