Just got my Muse DAC and burning it in after a few mods.
Most of the heat from the DAC is generated by the LM317T voltage regulator. It is cooking using a 12VDC power supply. I think that is the source of the overheat problem, especially in a small enclosure. Using a lower voltage power supply will definitely help significantly in reducing the heat given off by the LM317T. Also the tab of the LM317T is not solder to the PCB plate underneath. I applied some solder and it helps to distribute the heat to the other side of the PCB, away from the components.
The heat from the TDA1543s are minor in comparison. The stock heat sink and compound are not very effective. I mover the four 100nf capacitors to the other side of the PCB and replace the stock heat sink with a spare set of video RAM heat sinks, which work much better.
Added a couple of jumpers, shorting out the stock Silmic 10uf output capacitors.
The red power LED is replaced with a green one.