Converting +/- 48 VDC to +/- 24 VDC
I suggest a separate power supply or two DC-DC converters as the easiest solution. 

For audio you could use simple emitter-follower zener regulators, but the problem of burning off heat will still be there. Eg. (Q1 could also be a Darlington pair) 







simulate this circuit &ndash; Schematic created using CircuitLab

The same circuit, flipped with a PNP power transistor would be used for the negative supply, and resistors could be added in the collector to burn off some of the heat. The calculations depend on the current requirements. It's easy to find TO-220 transistors or Darlington pairs good for 60V or 80V. 

It's not inherently short-circuit proof and the efficiency is terrible. You could also use these as pre-regulators for 3-terminal regulators but that doesn't help much. 

The 24V suggests a relatively high power amplifier, which means the horrific lack of efficiency is going to be an issue.