Power Output

Yes if both are wired 2ohm and you have both positives and both negatives run to the amp.

I do not use nor do I tell people to set up an amp with a DMM I know people do it all the time and that’s their business if they want to take a chance on it being wrong.

I use an oscope for seting an amp. I use a DMM and a amp clamp to tell me how many watts I am producing or to match amps in cases where I am using 2 amps and 2 subs.

sqrt (600/1) or 24.5 VAC since that is what the amp sees and thus the voltage needed to make the power you want.

note you may not be able to achieve that with clean output since you may not know what the amp is truly capable of. some ratings are at 12VDC some at 14.4VDC some higher (trickery).

some DMM's don't read true RMS (cheaper ones wont). if your DMM is True RMS it will say so.

you can set your amp gain this way but that doesn't mean the adjustments end here. you still need to use common sense and listen to your subs. when they start making bad sounds, turn it down.