What cables can lower my forward treble.

Forward treble should be treated at the source, not through cables. You want to swap out the offending component until they sound perfect. Then start working on cables and power cords. 

Try Veritas. It does not add warmth, but it makes high-end notes smooth and liquid without compromising detail. I have Optimus (I²S) and Magnus (XLR).

I also tried the Cardas Clear digital (USB) cable; while it smoothed the high-frequency notes, it compromised dynamics and softened the low-end response.

I never expected cables could alter sound characteristics to this extent, but I am now convinced.

Just curious if you only started having this issue after adding the Hegel CD player?

I have the Dali Euphonia MS5's and I agree with knotscott, as I added felt around the border of the tweeter module and it does help with that tweeter high frequency edginess. And yes Dali's perform best with 0 degree toe in. 

@knorpi doing some RTA anaysis will save you the needless cable spamming. I'm hazarding a guess thatthe data will show clesrly areas of harshness