Taming the high frequency

Looking for ideas/suggestions to tame high frequency harshness. Recently installed a Lexicon MC 12 processor after my Krell decided to go to the electronic graveyard. Since I did not have this issue before I'm assuming the Lexicon is more revealing. My dedicated listening room is 15X23x8 and is treated with GIK 244 and 242 panels along the front and rear wall at ceiling junctions and Accurex bass traps in the corners floor to ceiling. Along the front wall behind the speakers are some decorative thick blankets for absorbption. No slap echoes anywhere in the room. Room is dual purpose H/T and 2 channel stereo listening with separate systems. Systems consist of Proceed Pre, Adcom 555II Amp and B&W 803d speakers for 2 channel and Lexicon Pre/pro, Polk speakers for H/T and Emotiva XPA amp. How can I diminish the high frequency harshness I'm experiencing? Any ideas or realistic suggestions?

@gillatgh - what speaker cables are you using?.

Your amp looks like a high current design?

If so - it may be experiencing an oscilation reaction with the speaker cables - i.e. if the cables have a high capacitance value it will staret oscillating - which will impact the sound

Selecting a speaker cables that has a capacitance of 10-20 pf/ft should eliminate the high frequency oscillation - if this is the problem

Van den Hul D352 or NAIM NAC A5 are two affordable cables that are low capacitance in the 10-15 pf/ft and they are pretty good performers.

By comparison - Cardas Golden Cross has a capacitance rating of 154 pF/foot.

A friend drove both his Ayre and Gryphon amps to destruction using high capacitance cables - not good.

Solid State amps having a High Current design will have this issue - whereas tube designs WILL NOT have an issue with high capacitance cables.

For high quality/resolution cables that will work very well with high current designs take a look at the KLE Innovations product line. I have reviewd many of theri products and they are first class and they work extremely well with my NAIM 5i - also a high current design.

Hope hat helps - Steve

Thank you all for your input. It's all well received and valuable. I was hoping for room treatment correction if possible as that is the least costly but........
I will try an old standby solid cable to see if there is any improvement.........or not since it is already available. Lord I hope I can stay out of the cable experimentation scenario.

I've found that harshness can be from various factors.  One thing you can try for cheap is to listen off axis (i.e., point the speakers ahead instead of towards your ears).  Also, quality of power can be relevant as well, you might want to look into power conditioning - I found that something like the Shunyata Denali definitely makes a difference.  With regard to your room treatment, I don't see anything that indicates that you have treatment at the first reflection points on the side walls or ceiling.  Also, I assume you have a think rug or similar covering the floor from the speakers to you because that's important as well for reflections.
Two things have helped  me , put a blanket over any TV in the room and
 turn off your wi-fi .
Problem solved by rearrnging some decor and furnishings. Thanks to all who had suggestions.and gave their opinions