Set ground reference of a 5v DC power supply to the middle of a 24v DC power supply

I have 2 isolated AC/DC power supplies. one generates a regulated 5 volt power supply and other generates a 24 volt power supply as you can see in the picture below:

I also have designed a circuit (the blue PCB above) that has analog parts that works with 24v and digital part that works with 5v. The analog part are some op-amps that I use for audio amplification so I need the GND reference of my audio (on my circuit) to be in the middle of the 24v. this reference GND is also used to be the GND of my digital circuit. so my main question is what is the best approach to set the GND of both 24v and 5v power supplies to be at exact middle of 24v rail. in other word, i have 2 pair of isolated 5v and 24v cables and I want to have these signals: GND(0),-12,+12,+5

you can see the main question in the picture below:

^{simulate this circuit – Schematic created using CircuitLab}

now the approches that I currently have in my mind is as follows:

1. use an op-amp:

^{simulate this circuit}

2. use a 12 volt regulator (7812)

^{simulate this circuit}

I wanted to know that if my approaches are OK? and if yes, which one is better? If there is a better way of doing this I would really appreciate any suggestions!