I realize that this response is a bit late to the game. I just wanted to give my perspective on what you're planning.
You didn't mention what command station you have - but you did mention that you'll have 6 engines running and you are in n scale.
The OG-AR needs 4 amps to make it work. So if you have a zephyr, for example, it does not have enough power to make the OG-AR work. That is, the circuit breaker/auto reverser function will not operate due to an insufficient current flow and you will pour up to 4 amps through the short circuit that the loco's wheels will create. If you have something with at least 4 amps, then it will operate. However, a short that draws 4 amps will be necessary to make that auto reverser do its job.
Different people like different things. For me, I don't like that 4amp spark. I decided for that reason to go with the digitrax AR-1. This can be adjusted to throw at 0.25 amps through 8 amps (ugh!). You have the PM42. So do I. I set up each of my power districts on the PM42 to be 2 amps max. Then I adjusted the AR-1s so that they switched before the PM-42 circuit breaker went off, so I imagine somewhere in the 1-2 amp range. It all works fine. This is not to say that the AR-1 is the world's greatest device, but I have 4 power districts and I have auto reversers on several of them and they all operate flawlessly and, for me, the currents involved are substantially less so that was a key selection criteria.
The 2 amps on each leg of the PM-42 has never been an issue for me; our small n-scale locos draw small currents and I often have at least half a dozen locos in a single district. Note I have no sound decoders and that would make a difference.
The point of the post? Consider carefully if you want to be tripping the auto-reverser with 4 amps.
