If I’m reading your post right, you can’t control any functions from the 6150, but any status messages from the 6160 appear on the 6150? If so, I recommend checking the wiring from the 20p to the 6150, and making sure the data terminals (The green and yellow terminals) aren’t in any way shorted. Then, make sure that the addresses are set and different from both the 6150 and 6160.
Hope this helps, and let me know if this isn’t still working.