Next to Barber's Adagio and some other highlights in the classical repertoire, there could be one added imo: the (late romantic) Adagio for strings by Guillaume Lekeu (January 20, 1870 – January 21, 1894), a Belgian composer and pupil of César Franck and Vincent d'Indy. By accident I heard this piece and was overwhelmed immediately. It was written when he was only 21, which is hard to believe given the emotional depth of this work: most probably an in memoriam of his teacher Franck.
The score says: solo violin, solo viola, solo violoncello, four violin parts, two viola parts, two violoncello parts and one contrabass part. But there is a passage with even also more divisi parts: 6x violin, 4 x viola and 4 x violoncello (which makes 18 different parts). A mockup of such a complex piece for strings is often not very grateful to do, but I simply couldn't resist the adventure, that's why. To prevent a muddy and non-transparent result I have chosen for solo instruments and small section patches (just like in all Youtube versions I have heard and seen). Eventually I have used a what I would call somewhat 'obscure' mix of instruments in this version for the small string ensemble. For the solo violin, viola and violoncello I have used the VSL Solo Strings, hence this contribution to the forum: this library is still unsurpassed imo.
This piece has been a great challenge in virtual instrumentation for strings for me. The extended handling of strings by Lekeu requires a.o. muted passages, third up to fifth tremolos (also muted) and moreover a very expressive quality of patches themselves and of course treatment.
Well, here is my "interpretation" of this piece: of course if I would do this piece again it would be different from this one, but it is just 'as presented'. The same for the mix itself btw. There are at least three different versions on YouTube, all played by real chamber string ensembles. This virtual version takes 10'22''. As you will notice there are many different tempi (and consequently lenghts) possible.
Comments are welcome. More info about Lekeu and this piece are on the same linked page as mentioned hereabove.