I have not read the whole thread here, but did want to share some thoughts on the passage that was mentioned in 1 Corinthians 14:1-4
I personally do not understand Paul to be introducing a 'privated prayer language' in this portion of scripture. I think if we keep it in context of all that he was dealing with in the Corinthian church, we will have better understanding of what he is actually saying.
Those in the Corinthian church who did have the gift of tongues, obviously were not exercising them correctly, and definitely not in humility and love.
(Paul addresses this thoroughly in chapters 12-13.) I think that he is trying to correct their errors, showing them that to begin with all things must be done in love, God gives gifts as He pleases and not everyone in the Corinthian church would have the gifts of tongues. Tongues had a purpose, and if those gifted were coming to their gatherings and using their gift in the wrong manner, others would have no understanding of what they were speaking, and they would in fact, be speaking to God alone. Note: he says... "BUT he who prophesies speaks edification and exhortation and comfort to men." Showing them that when gathered as a body, this was the preferred manner, the one gifted for tongues should use it for the purpose it was given, which obviously was for evangelizing the gospel. Otherwise, using them in church, he was only 'edifying himself' (vs. 4)