So, Singing the Past mentions that many of the tunes used for singing epic poems are melodically pretty flat, have stepwise motion, and span a fifth or a sixth. Hoppin says almost the exact same thing about the oldest extant Gregorian chants - they commonly span a fifth or a sixth rather than an octave or more. I suspect that, the more that I look, the more I'll find traditional cultures with poetic/musical traditions that fit this mold.
(Insert standard disclaimer about applying evidence from one culture to another here.)
We get folks on the lyre group who seem to think that playing melody on the six-stringed lyre is "lame" or too limited. Well, it absolutely is, by our modern standards. From the late Renaissance on, we've been conditioned to expect depth and texture in music - first, polyponic and then homophonic, as chordal texture started its reign of tenor. So by any yardstick used in the last 400 years, yes, the lyre is a thin-sounding instrument with few possibilities.
Of course, it's more than 400 years old. And, based on my admittedly limited research so far, I'm starting to be of the opinion that the desired sound would have been something primarily melodic and easily encompassed by a sixth or so.
Technically, I think the challenges come in cleanness of fingering and sensitivity to the instrument. When you have stripped down the sound so far, to a bare melody or melody with drone, you need to really have a clean, pure melody. It doesn't have to be complicated, particularly for epic recitation. But it can't be sloppy, with ragged intonation or uneven rhythm.
Rhythm. I don't know what the answers are*, but by golly, figure out your correct answer for this particular piece and then nail it down to the microsecond.
*Aside - matters of rhythm and note duration in very early music are extremely contentious. There are no known right answers. What I'm saying is, whatever rhythm(s) you decide on for a piece, they need to be executed with full commitment. I used to worry about playing the right notes. Now I worry about maintaining rhythm. A hiccup in rhythm is ten times uglier than a misplayed note.
Artistically... artistically, it's hard. The audience is conditioned to want more. You are conditioned to want more. The aesthetic the instrument belonged to... we don't really know it. Some days, it seems like re-creations will be interesting exotica at best and dry, clinical efforts at worst.
That's the challenge - to make the art sing again, to make the glad-wood speak to people, even though we may have forgotten how to hear it.