Wow, you're basedin North America, right?
This definetly isnt related to the Wi-Fi interface, but to electrics.
And probably you have a bad or picky PSU for the Soundbridge.
And maybe real old wiring/starters whatever.
I think the starter of the tube really causes some voltage spikes/peaks on the wires which cause the soundbridge's PSU to fail for a short period.
If you cant/wont fix the cause of this, just get a cap for the soundbridges PSU or a isolationg transformer. Probably a cap is enough. Sort of those you use for a car stereo to buffer for voltage loss during engine start.
de-u/c'd NSLU2 Unslung 6.8 - mt-daapd svn-1696