The cable connectors on the ONIX products are different but there is an adapter that would allow you to use an XP-9-20 transducer with an ONIX unit. The AS-1429
Is the adapter cable that you will need for this.
For your ONIX unit to work with the US2 you will need an adapter cable for it as well. Try looking for the MKR-US2-13 adapter cable.
http://store.minnkotamotors.com/media/d ... yChart.pdf
The ONIX units will connect to each other by use of an AS-EC-XXE Ethernet Connection cable, where the “XX” gets replaced by the cable length. They are available in 2, 10, 15, 20 and 30 foot lengths. So the part number for a 15-foot Ethernet Connection Cable would be AS-EC-15E. Be sure and measure the cable length needed by how the cable will run within the boat.