Just to clarify: The Optical and coaxial connections of the RS220 are not connected to a DAC in the way you might expect. The DAC, as with all digital transmitting wireless headphones, is located in the headphone itself. The fact that the power, DAC, amplification and driver are all stuffed inside a headphone's ear-cup and this all has to be relatively light is the main reason why they are so tricky to make and keep their audio quality competative with the highest quality wired alternatives. The fact that you can't add any other DACs or amps to the mix also means they're impossible to upgrade.MajorFubar said:I have the RS180. Absolutely satisfied. I couldn't get on with the 170s; they made my ears sweat, but the 180s don't do this. However being open backed they do leak sound a lot and don't expect any insulation from room-noise. They can be bought off Amazon for £169. May be even cheaper elsewhere. Unless you have money to burn, check that these will meet your needs before £400 on the 220s, because at least part of that money is used on the price of the included optical and coaxial DAC, which you may not need.