Len,Pat, I replaced my ST4000 with an X-5 several years ago and do not remember having to buy additional cables or a converter. I may have had the necessary cables lying around but what was the need for a converter? I also had a suite of ST60 instruments. I did have to acquire an NMEA Multiplexer as the Raymarine C80 chartplotter only has one NMEA input, I needed 3 (VHF DSC, X-5 Fast Heading and laptop to transfer routes/waypoints). I then sent the output of the multiplexer through an AIS to the NMEA input at the C80 and configured the port to 38.4 kb. Keep in mind that if you have a radar interfaced to your chartplotter and wish to benefit from MARPA (mini-automatic radar plotting aid, gives CPA) then you need to connect the X-5 computer to the chartplotter via NMEA, not SeaTalk. This is the only way it will function properly.
The new SPX-5 comes with a P-70 head not the older ST-6000 head which has been discontinued. The P-70 head does not do Sea Talk 1 or the old "legacy" system of Sea Talk....
