I agree with you. The fax in Elastix is not well explained nor supported. I have the same problem. It is not obvious how it works. I have also tried adminsparadise. The fax feature is better than here, nevertheless I came back to Elastix because some bugs in adminsparadise (call report, webmin ...). I think avantfax will be the key feature for Elastix, plus system administration through webmin.