The design that i have attached above is for 1A fir each of voltage level generated.
Then I would go with a linear supply as it's simple, low cost, and has low noise electrical noise if you are powering sensitive analog circuits.
I suggest buying a transformer with two isolated outputs and built two identical series adjustable series regulator circuits using LM317s.
For 24Vdc maximum output you could use a transformer with two 20Vac, 1.6A windings (transformer rated for about 65VA total).
For a cheaper approach you could buy two 24Vdc, 1A wall-wort supplies and connect the LM317 regulators to them.
A direct connection would give 24Vdc output and the regulator would generate any voltages below that.
You could place the wall-worts inside the case along with the regulators and run a power extension cord inside the case if you want to avoid have to plug in two wall-worts externally.
That way you will have two independent (isolated) outputs that can be used for any combination of two voltages at the same time (both the same polarity or opposite polarity, depending upon how their outputs are connected externally).
You would need to heat-sink each LM317 to dissipate about 28W (24W with the wall-worts) maximum.
For that a fan-cooled heat-sink, such as used to cool PC CPUs should work well.