i took a brief look at d-ne300 and d-ne20 SM's. first of all, they do not indicate explicitly how the power red. is done. 1) dne-300 fortunately the power amp (IC301, page 2/4) is pretty easy to find data on (the schematics shows Toshiba's TA2120FN, while component list Panasonics AN7531SA). it seems that it has an attenuation pin (pin 13 ATTSW). when it is disconnected from the ground, then the voltage gain drops by approx. 8dB i.e. approx. 2.5 times. perhaps that's the trick? dunno, as i dont have dne300, but dne900. 2) d-ne20 hopeless due to digital amp, the phones are directly driven by the system controller. mu gut feeling is that here it must be done with a software best, me