I was originally going to post this to the desktop amp forum, but then saw this forum which is probably more appropriate.
In reading various posts in this site I have run across references to balanced amplifiers and this prompted to me dig a bit further into these and the claims made for them. Certain aspects make sense. Balanced inputs have proven noise rejection advantages hence their widespread adoption in pro audio. Having separate ground runs for the left and right cans makes a certain amount of sense, removing resistance from the common ground connection would seem to have advantages though whether it is worth the hassle of rewiring is less clear.
Inside the amplifier itself things get a lot murkier. If you read the technical description of these units, what you are basically getting is a pair of floating ground amplifiers being driven in push pull for each channel. This design is used commonly in car stereo head units, where it allows for double the power on a 13.8VDC supply without going to the expense and space required for a DC to DC converter. You pretty much don't run into them much elsewhere.
Fully differential power amplifier designs employing bipolar power supplies have been around since the 70s (I have even built some from kits). In these designs, separate sets of devices handle the positive and negative portions of the signal so they are inherently balanced in nature. The promoters of balanced headphone amps (referring to the floating ground configuration with two completely separate amplifier sections for positive and negative) make the claim that using a balanced configuration results in twice the maximum swing and slew rate. While this is true, it comes at an expense of twice the parts count, and the same result can be achieved by simply creating a design with the double the supply rail voltage in the first place.
These balanced amps obviously aren't using the topology and space to save money as is done in car stereos. These units range from expensive to extremely expensive. So why are the companies doing it? Anyone seen a valid technical reason for this? I have a suspicion that it is simply a way for a company that already has a single supply, non-differential amplifier design to get more swing without going to a higher voltage true differential design, but maybe there is something I am missing.