Hello AudioGonners! Here is the story...
The DNA-2 has both balanced and unbalanced inputs but is not a "true" balanced amplifier, so there is a high-quality summing amplifier following the XLR balanced input. This sums the balanced input signal and feeds the unbalanced result to the normal input. This summing amp has a very high natural input impedance (multi-Megohm), so you normally use some loading resistors to tailor the input load to whatever you like. Well, given that life isn't perfect, some of the early DNA-2s left the factory without these load resistors installed. This lead to various performance problems when the balanced input was used, from hard, glassy sound, to instability and low-level oscillation. The problem was quickly identified and the resistors added, but that still left a few DNA-2s without their input load resistors. Sorry, but I do not have any serial number data.
It is easy enough to check your DNA-2 for these resistors. The load value chosen was 10Kohm, so you simply have to use a multimeter to measure from pins 2 & 3 to pin 1 to see if the resistance measures around 10Kohm, or is way up in the Megohm range. Please keep in mind that this relates only to the XLR inputs - the RCA unbalanced inputs are fine.
If you find that your DNA-2 is lacking these loading resistors, you have a few options. You could ship the amp to McCormack Audio in Virginia (www.McCormackAudio.com) for service, but this is time-consuming and involves the all-too-real risk of shipping damage. You could have a local technician attempt to do the work, but this involves partly disassembling the amp, and the DNA-2 is not exactly simple. My suggestion is to install a pair of small 100Kohm load resistors inside each male (amp end) XLR connector. A good technician (or your cable supplier) should be able to do this without too much trouble, in my opinion. How difficult this job may be depends on the specific connector used. Many cable companies use Neutrik connectors, and they are pretty easy to work with. Connect the resistors from pins 2 & 3 to pin 1 in both XLR male connectors. (I happen to be partial to the 100K load value, but the actual resistor value is not terribly critical, and values in the 10K - 500K range will work. Use a good quality resistor, though. The Vishay VSH series are ideal, but any good 1/4W metal-film will work.)
Finally, you can always send the amp to me for upgrade, and I will be happy to do it for you ;-)