I don't know if this has been mentioned before, but someone on a thread about the Tera player suggested trying a 75 ohm adapter with the ESW9s. These adapters are usually sold for use with a Ety ER4P as described here: http://www.ebay.com/itm/ETYMOTIC-ER4P-TO-ER4S-RESISTOR-ADAPTOR-3-5MM-PLUG-/290372905689
However, it has a nice smoothing effect on the ESW9s. I use an iCAN amp that has a 3D soundstage enhancement that adds space to the soundstage. Unfortunately, it also adds a bit of brightness by boosting the highs. The ESW9s sound great with the iCAN, but adding the adapter brings back the smoothness of the ESW9s while still allowing me to enjoy the 3D effect.
Anyone who wants to tone down the highs in their ESW9s might want to give this a try. The effect is subtle and does not seem to mess up any of the rest of the sound.
Do you find that it also reduces the volume A LOT?
It also increases the output impedance of your amp, reducing the damping factor and altering the frequency response of the phones.