I have been working on reverse engineering HymnSoft and creating a new client that works on the existing data. I am ready to release an early version. I am calling it TfosHnyh (hint: backwards). It currently parses the hymnsoft hymn database and displays the information. It also plays the hymns, both four-part, and melody.
It does not support the Psalms or the Canticles yet. It can also not quite output the MIDI data to an external keyboard. It might work for you, you can try it.
I am uploading the source for VS2010. You need the .Net framework version 3.5 to run this.
Another post documenting the database format is upcoming.