Do you even attend a Traditional chapel?
I would attend any traditional chapel had I the liberty, but at present I occasionally attend Holy Mass at a FSSP parish, which is where I asked the priest - whom from my experience with in the confessional, and hearing his sermons I greatly trust.
Because I know the SSPX says not to attend a Protestant service unless it's a wedding or funeral, and even in that circumstance they say you shouldn't participate in their prayers.
I don't disagree. Playing an instrument is not participation in prayer. Whether or not I am present and playing the organ does not affect their beliefs, it is a mere musical/auditory aid for many whose vocal skills leave much to be desired. I never join in their prayers; I refuse to even participate in the external physical gesture of bowing my head when the rest of the people are doing so at the "pastor's" orders.
So that being said, I'd find it hard to believe that an SSPX priest would tell you it's ok to play the organ at a Protestant church. There's no way you can do that without being subjected to the temptations of becoming a Protestant.
When I become attracted to idiocy, mediocrity, and melodramatic sentimentality that above *might* apply.
Seriously though, I pray the Rosary when I am not playing the organ for them. I hardly hear whatever they say. Plus, I have noticed that their readings from the Sacred Scriptures are almost identical to the ones I'm subjected to at the Novus Ordo.
Aside from that the only *threat* would be having a hymn stuck in my head after playing through 5 verses. But you'd be amazed the the same hymns you sing at your SSPX chapel are used by countless other Protestant churches (many of the hymns at least) and in fact were written by heretics.
No, it's not a sin to walk outside just because you MIGHT hear something such as cussing or gossip, but it isn't a sin to hear that unless you want to. You're drawing hyperbole conclusions from our posts. What we're saying is that you shouldn't subject yourself to people who deny the Church of Christ.
Are you a law abiding citizen of the United States?