Originally Posted by MrHifi
I fear that something quit in the preamp but I bought the XLR terminated cables in order to rule out a ground loop issue.
XLR "terminated" (adapter) cables won't solve the issue (if that's what you meant.)
*Actual* XLR connectors for pre-pro and amps are needed at each end.
Of course I can't actually recommend this, but another way, is you can eliminate the hum by cutting off the ground prongs (if you have 3-prong power plugs), if not...out of luck.
You probably already know all that, perhaps I misunderstood when you called them XLR terminated cables, because they do have cables like that, that basically adapt to RCA, but they won't eliminate hum. The thing that will eliminate hum, is true balanced XLR connections input to output, since they won't use the ground leg as part of the signal path. The 9.9 of course has XLR connectors on its end, for it to eliminate hum you need XLR on the power amp input.
If all that fails, the only other way is ungrounding the equipment to eliminate the paths for currents to circulate between connected devices. It's not safe, unless individual isolation transformers are used for each piece, to eliminate potentials between devices. There would be safety by permitting them to float so there is no potential to ground, i.e. reduced shock hazards. This is common in industrial equipment but I don't know of anybody who does this for home theater. Bottom line, you need power amps with XLR inputs. Hopefully you already have them.
As an anecdote, this was a real problem for me at one time, because I am using self powered, active studio monitors. The monitors themselves are pro pieces, (Dynaudio and JBL) so they had XLR inputs already, but my pre-pro did not. Line hum 60hz was a problem. That is why when I set out to purchase a pre-pro, XLR outputs was the requisite feature. The other major benefit to XLR is the higher voltage drive level. You have more input gain available on the amplifier. But until I had the Integra Pre-Pro (9.8), I had to cut off the ground prong for the power cord on each of the active speakers.