What cables can lower my forward treble.

You will likely find that speaker placement and setup will have much more sonic influence over different cables.  As well as placement and toe in, don't forget to try different rake angles.  If the speakers are raked back (leaned back)  even a couple of degrees that can diffuse the treble a great deal.  

@knorpi 

FWIW, I’ve used the Syn. Foundation XL power cords and a Syn. Atmosphere Euphoria digital coax cable with my Hegel H390's onboard AKM-based DAC  and did not find that combination to be bright. 

Try some Cardas Golden Cross ICs.  If that doesn't get you there, add some Golden Cross SCs.  Cardas hasn't made them for years, but there is a steady trade in this model on ebay and the audio sale sites.  They are always sought after so the good part is that if they don't work out for you, you can resell with minimal to no loss.  See also the thread on this model here--there was a recent post from another convert to the GC club.

While different cables do have specific sonic characteristics, you shouldn’t be fixing your sound with cables.

Acoustic treatments and positioning are your most powerful tools. Solving treble issues with cables was, for me, a fool's errand.