I use a different way of connecting both of my apc mini's.
I use BomeMT classic, TransMIDIfier and loopMIDI, or anything similar.
First of all I create two virtual midi "pipes" for routing the midi.
Then I use BomeMT classic to route the midi send by the second apc to another midi "pipe" so TransMIDIfier can receive its midi. (in the upcoming build of TransMIDIfier this step will be no linger needed)
Then I use TransMIDIfier to route the midi send by the first apc to channel 1 of another virtual midi "pipe".
Next I use TransMIDIfier to route the midi received by BomeMT classic to channel 2 of the same midi "pipe" as the previous step.
In your case, use TransMIDIfier to route your midi send by your Launchpad to channel 3.
I hope this will work!
If not, feel free to ask me any questions about your problem!