speaker cable and IC's to dim brightness in system

My first recommendation would be the Cardas Golden Reference for speaker cable. In my opinion the Cardas Golden reference speaker cable has everything you are looking for.
My Second choice with your system would be the Monster 2.4 speaker cable.
You may find the Monster 2.4 speaker cable very engaging with the Krell amps. I owned a set of the Krell FPB/250 mono block amplifiers and found the Monster 2.4 cable to be very engaging.
Also, I would take a look at the power cords and line conditioner you are using and perhaps make a change.

Many folks have commented on Krell's and B&W's sounding very dynamic, detailed and punchy initially, which is what draws them into the combo, but in the long run they end up suffering from listening fatigue. I'm sure that finding "synergistic" cables can "band-aid" the situation if you are basically happy with the combo but dislike the problem with brightness. Otherwise, i would suggest selling the Krell and continuing your search. At the price that you paid for the TAS, you won't get hurt on it in the least.

I'm not passing judgment on the Krell or B&W's, only responding to your comments about this specific combo. I recommended moving the Krell rather than the B&W's as i know that you also have B&W surrounds along with your mains and moving the Krell could help put some extra money in your pocket for such a search. Sean
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Audioquest Sterling. Smooths out the brightness and extends highs beyond without dulling . Brings midrange and bass into focus which creates the illusion of less brightness. I've heard them on many systems and can't find anything I like better

I really agreed with Sean's comments. No interconnects in the world would tame the Krell which is giving you that aggressive sound. Your 802 is one of the very best ever made. The Krell is not the kind of amp that will give you long term satisfaction. I had 802 before and I found they mate with tube amps very well.

I have found that the MIT line of cables did a good job diminishing the brightness of my Thiel 3.6's with solid state amps. They tended to take all the high frequency detail, and 'space it out' a bit temporally- not sacrificing the detail, but keeping it from being too bunched up and screechy.