Unfortunately, the design engineers decided to dual purpose an output without understanding the consequences. The PHONES/DIRECT OUT provides a stereo signal to the tip and the ring of a 1/4 Jack when inserted into the connector on the back panel. This is fine for listening with headphones but absolutely WORTHLESS when connecting to any mixing console input.
Almost all mixer inputs accept BALANCED audio signals and when you send a STEREO signal to such an input you will only hear the audio that is not common to either channel. Mostly it will be a really crappy, low level signal that is impossible to use to anything. The easy fix is to lift one of the conductors on the cable (tip or ring) and leave it unconnected to anything. A more complex fix is to combine the leaft and right channels to make a mono signal and put it on the tip of a cable sent to the mixer and leave the ring unconnected.
WHY?
Because BALANCED audio format is one of the coolest tricks around. A balanced output has the guitar (audio) signal AND the inverse of the guitar (audio) signal both on the one cable. Signal on the tip (or pin 2 in XLR) and inverse of the signal on the ring (pin 3 of the XLR) . When these signals are sent to a BALANCED INPUT, the signals are SUBTRACTED from each other to produce a signal with twice the gain. This is all done to eliminate the noise which will be a positive signal on both conductors.
Say the signal is 2 volts and the noise is .5 volts. You get 2 - (-2) = 4 for the signal and .5 -.5 = 0 for the noise. brilliant stuff because it is so simple.
So when you plug your DIRECT OUT into a balanced input (almost all mixers have balanced inputs) you get LEFT SIGNAL - RIGHT SIGNAL = almost all the good stuff gone!
I was shocked that a great company like LINE6 would pass this off and even tell you tpo use the DIRECT OUT to record. Really a remedial design issue that should have been caught before they made the amps.
peace