Monoblocks out of phase on dedicated line

Poor Man's Dedicated Line. Any thoughts?

The problem of using both phases in one system is if a fault occured.
Then you would have a 240 volt possiblee fault if you touched the wrong things, it it might also destroy some of your other stuff.
240 volts is a lot.
So that is the reason to use only one leg
The interconnects from each amp go to ONE preamp, so one or the other will be taking the chance for the 240v fault.

I see. Which phase should I use for my 3 dedicated lines? I measured both phases without any appliances on them and I get around 122v in one phase meanwhile the other phase is 124v/125v. Thanks

What you want is the one with the fewest appliances.
I would bet that is the higher voltage phase.
Some appliances cannot be avoided, like 240v AC or Stoves. but refrigerators can and should be avoided.
Anyway, I would naturally jump on the higher voltage line as the one to use.
You should be able to grab two of those higher voltage dedicated 20 amp same phase line off your incoming electricity.
Use one for each amp, and part of each of those lines for all else. half all analog with one amp, the other half all digital with other amp.