What are the switches doing? Switching the alternator between output 1 and 2? Orions are Battery-to-Battery chargers, if the alternator is connected to the Orion input directly, without a starter battery connected, then the alternator output voltage could rise to the max its capable of, which could be more than the Orion can handle.
Also, only the port engine can charge the house battery.
Personally, i would use the switches only for maintenance, and instead feed a diode combiner off of the two engine batteries, which then feed the Orion input. So you can charge the house battery from both engines but still keep the two seperated.
The manual for the XS gives recommended cable gauge and maximum recommended cable run length. If I recall correctly it prefers a short length from XS output to house battery and up to 5m on the input side.
I agree with the point made above about the switches. Disconnecting a running alternator from its battery can cause a voltage spike and alternator damage. Such disconnect happens when you flip the switches in their current configuration. There will be a moment in time, as the action rotates, when the alternator is isolated from both the start and house batteries. Safe to do this before you start the engines but more risky when an engine is running.
Use the motor alternators to directly feed their respective start batteries and then connect the XS to the start battery sources using one of your 2way switches or Cyrix combiners.
I prefer the Cyrix to a diode based setup because there is less volt drop and this will enable the XS engine run detection system to be used more beneficially.
The switches disconnect the motors and the batteries when the boat is not in use. The space is tight and I didn’t see it at first but the 2nd switch may also be connected to the house battery, i’ll have to recheck. When both switches are on, all 3 batteries are charging from motors alternators. I wouldn’t switch off while the engines are running, only at the end of day. Planning on 6AWG wire since my distance is <5M . My goal was to change out the house battery with a minimum of rewiring because I have limited access.
With the Orion in place, the alternator will either way be isolated from the house battery. Even if the switch is in place to supply the Orion before engine start, since theres no battery connected to it, the alternator output will most likely not just spike but stay high.
The voltage drop over the combiner diodes is negligible in this case (could also use an ArgoFET combiner), since the Orion will simply boost the input voltage up to charge the output. Using Cyrixs in this work as well, but adds no benefit while also adding mechanical/moving parts