When I first got my Velodyne sub, I had a lot of problems with a 60-cycle hum too. It took me about a month of messing with it to figure out what was causing it. It turned out that it was related to my cable box--apparently cable systems are NOTORIOUS for creating ground loop problems when connected to a stereo system. My solution involved connecting the cable box to the receiver with an optical TOSLINK cable instead of the digital coax, AND putting a ground loop isolator between the outs of the receiver and the ins of the sub, AND putting the cable box and TV on their own surge protector, separate from the rest of the system. My sub would even hum if it wasn't hooked up to the receiver like yours, and in the end it was almost all about the power--NOT the cables, the components or the sub itself. Connecting the cable box to the receiver via digital coax introduced a little more hum to the sub AND made my main speakers hum too, but the sub's main hum was pretty much all caused by the power connection, when it was on the same circuit as the cable box and TV. Most AV gear, apparently, has a completely different kind of grounding topology than most stereo gear, and causes all sorts of problems...
I would suggest putting the sub on it's own separate power strip--get a good one with fast clamping and a high joule rating. It doesn't need to be a super-high-dollar unit like a PS Audio, but I would at least get a heavy-duty Belkin or something. Also, if you've got your cable box hooked up to your stereo--either with a digital or stereo analogue cables--try connecting it instead with a TOSLINK (plastic fiber optic) cable. This will help isolate the cable box from your stereo system.
You might also consider getting a ground loop isolator. I was using an inexpensive unit I got in a car-stereo shop, and it seemed to work well.
If none of these things work, go to the hardware store and get a "cheater" plug (one of those 3-prong to 2-prong adapters). Even if your sub has a 2-prong plug, using a cheater plug sometimes helps for some reason. It's not an elegant solution, but sometimes it's the only thing that gets rid of the hum...
Good luck sorting this one out. A 60-cycle hum is almost always related to ground loop problems, and finding a solution can be one of the most maddening bits of trouble shooting you'll ever experience in the stereo world...
Welcome to to the forum, and hopefully we can help you get your system sounding great!
..............................• Martin Logan Scenarios, Logos • Realistic Minimus 7's • Velodyne F-1500b •
• 2 Ch. Rig • Carver C-4000t • Silver 7t's • Krell KAV-300i • Oppo DV-981HD • Benchmark DAC1-USB • MacBook Pro 17", iTunes •
......• Technics SL-1350 turntable with Sumiko headshell, leads, and Bluepoint cartridge • Martin Logan Sequels •
.........................................................-+-Click Here to see my system-+-