HARMONY has just had MusicXML Export added (although some scoring information is not fully exported yet, such as note beaming), and I am working on Import.

HARMONY registration is set at $25 or equivalent.

(By the way, you have full control over timing of all notes! Unlike some packages, apparently)

Harmony also does transposing (notes AND chord symbols), and has a handy Reel to Hornpipe converter!

(Many hornpipes have been wrongly notated in abc as reels)