Ground Loop Hum with balanced XLR cables only

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.

I am (was?) battling with phono 60 hz hum in my system, too. Spent a lot of time swapping out components, star grounding, floating, relocating, cleaning connections, etc, with no luck. Yesterday may have been an epiphany (not 100% certain just yet). I think it may be a defective IC (RCA). This particular IC was previously defective (humming and shorting out; OMG the loud, crude noise it could cause if wiggled the wrong way), and I had it "repaired" at the factory. I reinserted it in my system concurrent with upgrading my phono stage, got the hum from the get-go, and assumed it had to be the phono stage I had just acquired. Finally, yesterday, I swapped out the IC with an identical model of the same manufacturer and the hum appears to be gone. Now, to be certain, I need to reinstall the aforementioned phono stage and see if the hum remains gone (I had used a full function pre to do my most recent sleuthing, which also had hum, so I figured the phono stage is not necessarily the culprit). My belated point is this: In my experience, ICs can and do go bad, and can cause hum or just plain short out. They are, IMHO, part of the investigative process and should be evaluated and tested when tracking down a hum.

Article by Bill Whitlock, Jensen Transformer on ground loop hum.In depth and informative.

Just got back from much needed vacation and just catching up on all the responses. The XLR cables are from Signal Cable and I spoke with the cable builder Frank and he assured me that the cables are wired correctly. Now of course I could switch to single ended cables (RCA) but I'd like to keep the XLR cables if possible. I'm going to try and lift pin 1 on the input side of one of the cables and see if that works. I'll keep everyone updated.