The SPX-10 computer was always a tricky system to get to play well with nmea 2000 when it was setup originally as setalk 1. I believe you are going to have to setup a Raymarine seatalk ng backbone with their setalk 1 to seatalk ng converter. Raymarine Part # E22158
First step is to run all the seatalk 1 equipment in a series into the yellow port on the seatalk 1 to seatalk ng converter (Including your ST6001 AP Control Head). You may need a setalk 1 junction D224 if you run out of ports. You are no longer running it in a series to the SPX10. It will not be connected to it.
Now all of your seatalk 1 devices will be talking nmea 2000 language. Your SPX 10 was configured to talk to everything via seatalk 1 or seatalk ng (nmea 2000). The SPX10 had a special stealk ng cable that plugged onto its main board. Connect this into one of the white ports on the E22158 converter hub. If yours is lost then Max Marine Electronics still has plenty
This cable is used to connect the X-5 Course Computer to the Seatalk NG backbone. The cable is new with factory tie-wraps, the bag may have a shelf rash
maxmarineelectronics.com
**Now turn the switch on the SPX10 above the seatlk ng port plug to off. It is possible for the SPX10 to power the seatalk ng network, but you do not want to do that here.**
Plug the one of the blue terminator plugs into one of the blue ports found on the ends of the converter hub.
In the other blue port use a setalk ng to nmea 2000 backone converter cable to jump over to your nmea 2000 network.
You now have one white port left on the hub. This can be used to plug the provided red power cable into the hub to power the network. I assume you are adding this converter hub into an already powered nmea2000 network so most likely you will leave this port empty.
In this setup everything will talk to each other properly. If you need a diagram let me know and I can make one up. It is probably the only way I can think of where you will be successful.
The SPX10 had information limitations on sharing what came into the system. What I described above puts everything on the nmea 2000 network and does not pass it through the computer first. The SPX10 is grabbing everything it needs through nmea 2000 now. This includes what it needs from your plotter to navigate to waypoints.
I would download an SPX10 manual for reference as well. I am sure it still available on the website. If there is any issue after doing what I described above then I would factory reset the Raymarine AP system and do your dockside setup seatrial etc from scratch. It may be looking for something on the seatalk 1 network that is now on nmea 2000. I can't remember if it will find it automatically.