i think this is a "do the ends justify the means" question. and we all have absolutes where we say no and ones where we say yes. Its the subjective stuff where we dont disagree on. We dont agree on some stuff and thats ok. Maybe we are all called to be in different places, which is why we may have different methods.
Just because I put my feet up on the coffee table at my house, doesnt mean I can come to your house and do the same. And rather than trying to debate why i think you're wrong for not letting me do that, why dont i respect it, because it is YOUR house.
I respect everyones opinion here and I do believe there is an acceptable level (the B3 and other modern instruments, even microphones and sound systems, recording equipment, etc, because those are "worldly" too, and if we wanna be technical, letting unsaved folk in your church is worldly as well). But we all just dont agree on where the line is drawn, and we all never will.
In that respect, I agree with Jeremy in that if you gotta say to yourself "am i crossing the line?" its best that you leave it alone. There may be a reason why you are asking that question. And if its right and its something God NEEDS you to do, best believe that God will open up your understanding, and that wont be a question for you any longer.
So just like if playing a song leads someone to Christ and you feel thats right because you brought in a soul, if NOT playing that song brings someone else to Christ, the person that didnt play the song is no LESS right because they brought in a soul too. And we should look at it that way, because some people are drawn to Christ because certain things are present, and some are drawn to Christ because certain things are absent. And if those certain things overlap, then we are going to be in disagreement, but we should follow the path of those we are led to reach.