I managed to get both guitarsignal and an MP3 coming from my Samsung tablet. I use a mini stereo from the tablet (audio out) and first put it in a mono adapter jack like this one: http://www.stofzuigerzakken-on…nts/media/verloopplug.jpg
Sound is coming on one channel of the headphones. But it's a stereo recorded MP3 and that means that the solo on that mix is far away, almost not audible.
The same if I use a stereo adapter jack like this one: http://www.obibouwmarkt.nl/med…d27136e95/0/0/0011728.jpg In this case it's reversed: the solo is well audible but the rest is far away.
Is there a way to get the same stereo sound from tablet into the alternative input (stereo or mono input?) and mix it all together with the guitar signal on one ( or better) on both left and right headphones speakers? Then you can benefit both! Volume mixing is no problem.