External GPS for a78 (E70203)

I would like to connect my a78 to an external GPS receiver. I have an existing NMEA183 GPS but I do not see any way to connect it to the a78 or to my existing SeaTalk 1 network with GPS (see note below regarding my existing SeaTalk 1 network) I have read the documentation and it appears the RS 150 is the only GPS which will work.
Question 1 - is that correct?
Question 2 - To connect the RS 150 can I use a A06064 SeaTalkng 5-way Connector with the RS 150 connected to the A06064, a SeaTalk ng power cable connected to the A06064 and the a78 connected with a spur cable to the A06064?

Note about my existing SeaTalk 1 network. I have a complete existing array of Raymarine SeaTalk 1 instruments which work great - Pathfinder Radar, GPS, ST60 (wind, tridata, etc.), SeaTalk 1 to NMEA183 converter, and also an ST 6000+ Autopilot with type 2 linear drive and type 300 course computer. When I purchased the a78 the marine dealer said I could connect the a78 to my existing SeaTalk 1 network using the SeaTalk to SeaTalkng converter which I purchased. But the converter documentation in bold type says you can NOT connect the converter to a SeaTalk 1 network with a type 300 course computer. Is that still true?