Two things, Bob. First, its not quite right to say that non-EPers say nothing in regard to what is and is not acceptable as worship. For one thing, the class of "non-EP" would include anyone and everyone who is not EP, including the likes of John Lennon and Cat Stevens, if you get my drift. But for another, those who are Reformed but non-EP have a completely different category in which they discuss this, so you generally won't find written essays on the subject of "non-EP". Instead you will find a lot under such titles as "godliness", and "holiness" which would assume the discipline of writing songs along with other disciplines. J.I. Packer and F.A. Schaeffer come to mind.