Those are distributed on the net by our friends at Corpus Christi Watershed ( http://ccwatershed.org/ ), so we at CMAA aren't in a position to speak for them, really.

If I understand aright, no permission is needed to perform a work at Mass, but streaming the performance on the net probably requires permission. I expect the composers would be generous about it, but out of respect I think you should ask.

Some of the composers on that site mark their scores with a Creative Commons license, which may make permission automatic under some conditions. Are the works you want to use CC-licensed?