Went to Radio Shack last night and asked if they had a DC-DC converter for
24V-6V. I was told by the somewhat surly person behind the counter that they
didn't exist. However, I also needed a 12V-6V converter (a spare for the
car), and upon reading the package, it said: INPUT VOLTAGE 12-24 VOLTS!

So, it looks like the Radio Shack unit should work anyway, which would be
great since it would eliminate carrying an extra battery, making my own
unit, or using an invertors. Anything that means one less cord and two less
connections is a positive move in my opinion.

The XM radio works great in the cockpit as well as at home. The sound is at
least CD quality and the unit and antenna are small. The reception was also
perfect. I'm waiting for a panel mount that will also encompass the weather
data that interfaces with MFD's.