A short circuit, is a circuit without resistance.
Might be nice to know a way to remove all resistance to flow.
I understand you concern is whether these things block the flow of qi. No they do not. In the early examples you try passing qi through a table top. In the upper levels you direct qi to people at great distance. So your plate will not cause you problem for the qi. Is it the best practice? I really don't know, but I don't think it is worth the amount of concern you already have.
Using head phones is fine. Especially in the beginning as you are learning the meditations. It can also help you maintain you meditation focus.
Master Lin also mentions that sound can augment our exercises, and he has meditation music to help. I know that at times this music has resonated incredible with me, during a meditation.
So I would say the headphones are somewhere in the better portion of good, better, best. Use them until you feel you are guided to some other practice.
You are perfection.
Iam2