I would note that the Bax is a Sonata for Harp and Viola. The harp part is mammoth, and even for you, might take six months or more to get a handle on. It is a great piece.
I would suggest:
Henk Badings: Cavatina, very difficult to finger, very atmospheric
Caltabiano: Lyric Duo,Very well written for the harp, rhythmically difficult, a lot of 5 against 4 or other combinations, somewhat tonal but extreme, dramatic, can be highly effective, was premiered by Catherine White.
Glazunov: Elegy, not easy, very lovely, hard to read because the print is too small. You might want to get the Belaieff edition for viola and piano.
Gounod: Hymne a Sainte Cecile, don’t know it, but if it’s Gounod, it must be goudenough.
Houdy: Suite, don’t know it, but he’s a pretty fine composer
Ravel: Pavane, needs no recommendation
That’s all for that catalog, so that leaves room for lots of Baroque and Classical pieces.
There are also the 24 Preludes for Viola d’Amore and Harp by Casadesus, in every key, which are very nice, neo-classical sort of pieces. They may be adaptable to the viola, or perhaps you can work with a violist who can play d’amore. In that case, you should get in touch with Joan Ceo, whose husband is a violist/d’amore-ist, and who have a lot of repertoire together.
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