I used a LM317T in my box to drop the voltage for the jb3 Andrew. Here's how I understand it.

You can use it to do the same for the Edirol R1, you just need to use different resistor values.

Anyways, to figure out what resistors you need to use, you use the following formula:

"Vout=1.25(1+R2/R1). R1 is fixed. so, various Vout can be achieved by adjusting R2."

R1 must equal 150 ohm

R2 = X

Vout = 3v

Solve for X.

Looking at what's commonly available (Radio Shack Stock) R2 can equal 220 ohm. That'll give you (if my math is correct) a voltage of 3.08 Volts, which should be within the tolerances of the R1 (check the manual first, though) I would be concerned about the heat built up in the box though, as the bigger drop in voltage you get, the hotter it gets (or so I've read.) Anyways, hope this helps. Note: I'm not an electrician, and I wrote this at 1:30 am. Follow these directions at your own risk!