Take cuttings of firm new growth apply 0.2% rooting hormone stick in well drained soil & mist taking 25-60 days to root.
It would help if you described the methods you have used & maybe we could better suggest changes

Do a Google search for, plant propagation + stooling. With a bit of reading you should quickly understand 'stooling'. I would rather have you read mulitiple discussions on the subject than give you just one site. I did note that the easily understood stooling method described by R.J. Garner in his book "The Grafter's Handbook" is listed there. This is a British book published in 1947 that should be in every pro's library.

It is common for blueberry growers to use the stooling method to increase stock. Can be used on most difficult to root shrubs. So, you have three methods; seeds, rooting under mist half-ripe cuttings in summer and stooling. Although I have not tried to root Edgeworthia, based on experience may I suggest stooling should be the easiest.

To Viorges:I have made cuttings in early and late spring, in midwinter and in late September. I have used all 3 levels of Hormodin and used peat/Perlite, Peat/sand, Vermiculite/Peat, Vermiculite alone and both sand and peat alone. In all attempts bottom heat was used. I have also tried the toothpick method and air-layering. In summation, cuttings made just prior to leaf opening seem to be best. I might add that I have rooted hundreds of shrubs, perennials, and annuals with great success.I do not have access to a mist producer; perhaps that is the secret.