Hi Bub,
Sound signals are AC. The gain of the signal is measured in volts. It's an axiom of audio design that higher voltages on rails allow for higher voltage swings on the analog signal path.
So if you take, for example, a AKM brand converter and place it an brandX appliance that is powered by a 12vDC external power supply and compare it to an appliance made by the very same brandX that happens to be powered with a 24vDC internal power supply you have a circumstance where the difference is easily quantifiable.
You can send 12vDc into an appliance and step it up to something that provides more head room... but you'll require more current which is costly... so you don't often see that type of design unless portability and battery operation is a high priority.
Most solid state components used in active audio electronics are easily capable of running between 5vDc to 48vDc. The greatest amount of headroom will be realized when the device has all the voltage it can use but it's a lot cheaper to run the device on lower voltages... especially if you can find an acceptable sweet spot that people can be satisfied with... so lots of gear is produced with lower voltage designs and narrow ranges of suitability.
The audio range itself is extremely narrow and limited compared to the spectrum modern electronic devices can work with, how ever it is the low frequency ranges, the ones that sit right in the audio spectrum, that require the most power to maintain accurate representation in reproduction. The easy way to make sure the low frequencies get printed accurately is to make sure there is plenty of power. The most efficient way to deliver power is with a supply of relatively high voltage.
If you want to hear differences in converter appliances listen in the low and mid ranges where the actual hard work is done.
best regards,
mike