I'm a newbie here so hi everyone! I'm mostly into the arcade restoration hobby. My current project is trying to mix stereo sound from mp3 player with the 4 channels game sound output. The circuit I made here works but I have two issues. The mp3 player level is too low and when I connect the mp3 player, I notice the game music level will lower slightly. I use all 10k resistors. Do you have any suggestions as to what I should improve? Change resistors, add capacitors? Thanks.