Brian,
Did you ever find a solution for this?
I just had this problem the other day. I plugged directly into someone's bass amp (they all seem to have built in DIs these days, direct outs), but I wanted to use a fourth mic and got paranoid that if I turned on phantom, it'd fry the guy's bass amp? I kind of doubt it considering the whole point of that direct out of the bass is to negate the need for a DI isn't it? So, I'd think it was designed to plug into a snake, etc., that might very well have phantom running down it (although most SBDs let you turn that off I guess, but some snake boxes are self powered aren't they?).
Anyway, if I could find an inline phantom-blocking adapter, seems like that'd have been the safest thing to use, but I can't seem to find anything like that on the web and this thread never posted a resolution except for homemade (which isn't something I'm capable of, lol)?
Unless someone could tell me that the direct outs on all bass amps will block phantom and not fry? I do that trick all the time, and yes I know it's a dry signal, but I get plenty of wet bass off my main stereo pair when I do this trick (for acoustic jazz recording).
Any help would be appreciated, thanks!