All well and good, but (as much as I don't like proof-versing) you should consider doing a word study on the Greek κοινωνία (koinonia). Particularly in light of 1 Cor 10:16:
The cup of blessing which we bless, is it not a participation (communion - koinonia) in the blood of Christ? The bread which we break, is it not a participation (communion - koinonia)in the body of Christ?
When you hear the words of the Apostle in 1 Cor 11:24-26, where we are commended to do this as often as we drink together of the cup, I'd say the founders of Christianity did not only know something of this -- I would say they were the prime movers of this.
Never proof-verse with someone like that. My “The Church of Christ” aunt likes to do this with my Catholic husband. She never wins, but thinks she does. My favorite episode was when she was trying to justify why we should not invite the Jews in his family to our wedding. What could we do but laugh?