Because of audio routing on the external PTT and how it interfaces, you would be better off configuring your 4010 local control card for high impedance and paralleling the connections on the rear connection to the MotoBridge. Remember that the Astro25 radio does NOT like having its audio grounded on the receive side, so you may need to use an isolation transformer or even an iso and a reduction pot to match levels close enough to be within the gain range for the 4010.
Do NOT overload the inputs to the 4010 card, and the best way to adjust the input AGC knee point is to use an analog channel in the XTL and set the 4010 from minimum until just where the gain levels off at the test point when you are increasing the pot, then back it off about 1/2 a turn. Then the AGC compression knee will work correctly for your console input.