I use Tux Guitar for 2 days know and love it already! For me, it is the long searched missing link between Reaper and Lilypond. Hartley Mays has made a mod of Tuxguitar which makes it possible to import midi directly from Reaper.
But I´ve experienced a problem with midi import in Tuxguitar: If the duration of a note exceeds its measure, the note will be cut instead of beeing tied to a note of the next measure.