I varied the voltage from around 9 VAC to 18 VAC, it did little to change the current.
I tried an older RailSounds board on the old ERR RS Commander power base, it got basically identical results. I did test some older conventional board with the ERR Sound Converter when I was doing the beta test several years ago, none of them draw more than a couple hundred MA in any operation. I think most of the energy consumed is actually in the amplifier circuit for any of these boards, so I don't think older boards would necessarily draw lots more current.
Without an actual board to look at, it's pretty hard to suggest a specific cure, but I'm sure this should be pretty easy to do for most audio boards. It would be interesting to see what the board does when the track voltage is removed but it still has internal DC power.
Depending on how long you need to hold up the power, a larger filter cap may be the path of least resistance.
