Headphone Out vs. Speaker Out - Distortion Difference/Troubshooting

PreCd

I have been doing some troubleshooting on my 2-channel system. I was wondering if anyone has ever noticed the difference in a reference piece of music while listening on headphones vs. their speakers? With all the enhancements I have done lately, spiking the speakers and room treatments, the weakness in my system is being revealed. Mostly bias setting I believe at this point and I have been troubleshooting with my headphones. I have a little distortion on some pieces.

I have been using Steely Dan: aja and Diana Krall: Live in Paris. Mainly the latter. On track 6 on the Krall album at 4:06 on my player, the piano distorts on a few keys. Briefly audible. So I throw on the headphones and lo and behold sounds good there from my CDP headphone out. Sounds good at the preamp headphone out also. I got most of the distortion out by adjusting the bias using the aja album, Track 2.

Using the headphone out seems to be a viable procedure to trouble shoot such a problem. Any input would be appreciated.

P.S. I also run out to my car audio system to see if the distortion happens on the Krall track and it is there although not as noticeable. Stock sound system.