Update to previous post. Fiio E17 drives 2 pairs of Koss ProDJ100 phones with no problem at all.  

I have the Koss ProDJ100 combined with recently purchased FIIO E17.    On my Win 7 PC with RealTek audio the headphone output is sorely lacking in power even with these 38 ohm headphones.   The FIIOS was $139 from Amazon and arrived in 3 days. It has totally changed my listening...