an 8x8 audio interface would be good (thuis means you can record 8 things onto 8 different channels on your daw (or 4 stereo things)
4 inputs for 2 gameboys
4 outputs for 2 eqs
4 inputs for the eqs
BUT if you are using a computer you really can get a much better EQ for free on software than you will get on a cheapo behringer thing (no doubt hardware is fun and nice to play with though) so if you don't have the hardware you can get away with a 4x4 which are cheaper and smaller if you want
buying an audio interface CHANGED MY LIFE:)