1) Spyra is nothing like Epiweb. The former is an absorbent fabric, the latter is like a non-absorbent scrubbee pad. I think you meant to say that it's like Hygrolon....
2) Folks use the fabrics to cover rigid substrates, then plant the fabric. Epiweb is a good option.
3) I think it's wise to put sphagnum over the roots, not under. Most of the time, when I've put it under, the root grow into it and never attach to the substrate.