In that configuration, Sends 4, 5 and 6 are all directly connected to the output of loop 3, so they're getting the return of the last active loop, or the output of the buffer if no loops are on. With nothing plugged into their returns, the three sends will be in parallel.
If you split the insert loop, you'll get two buffered signals at the loop send jack, one on the tip and one on the ring. The signals will come from whatever's right before each half of the insert loop in the loop order.
Send 4, 5 and 6's output impedance is the output impedance of the last pedal that's turned on in loops 1-3, or the output impedance of the MEGX's buffer if loops 1-3 are not turned on.