I have a PreSonus HP2 with the dual 1/4" TRS/5-pin XLR input cable. I want to use it to mix the analog stereo headphone output of my Panasonic SA-HE100 DAV Receiver with the stereo output of my Universal Audio Ox Box. The headphone output on the receiver easily drives my DT990Pro Open-back Studio Monitor Headphones (127-Ohm), but cannot drive either input channel on the HP2. There is no problem with the Ox Box stereo headphone output driving the HP2. I'm using the 9V power supply that came with the HP2.