Yes you can do that. On the board (on the left right above the bread board) there is a little solder pad labeled "mix". You can take the audio mix from there, run it through a filter. The next part is a little weird. Just to the left of the audio output jack there is are two solder pads. One is labeled "O" the other "I". "I" is connected to the mix, "O" is connected to the jack. Then there is a little lead connecting the two. Use a knife to cut this connection... Now you can take the output of your mix and connect it to the "O" point. This will rout your filtered signal to the output jack