Ground Loop Hum with balanced XLR cables only

The three pins that make up the "XLR" are not always wired the same.
Consult the makers.

One or all of the XLR cables might be wired wrong/different (pin wise) which would make the ground pin not connected correctly.

Usually it's the other way around. RCAs will create hum/noise and the XLR will solve it.

Its probably because you’re running the amp balanced and the preamp SE. I've seen this type of hum several times. You may have to use the SE inputs on the amp. However, I've been able to fix the problem in the past with cables. Audioquest IC's with DBS was the cable that worked.

Perhaps you have ground loop. RCA cables' shields are normally grounded on one side only, while XLR cables shields are grounded on both sides. It makes for better, shorter return of the noise induced currents but creates a lot of ground loop problems in recording studios that exclusively use XLR. I would try to connect together and to the earth ground all the chassis in star fashion (no daisy chaining) but I'm no "Hum Whisperer"

The Integra 9.9 has XLR outputs as a "convenience" feature, but is not a truly differentially balanced unit, to the best of my knowledge. As a result, other connected components may not be at the same ground potential, and a ground loop hum could result.