I know the music David Popper, one of the foremost cello virtuosos of his time, and one who in his later years regularly performed with Jenö Hubay and occasionally with Brahms, mainly through the virtuoso etudes and other trinkets played as encores by all the cello virtuosos in the world starting with Janos Starker, but looking at this catalog of compositions (almost all centered around his instruments), I wonder it there isn’t more and better to him than that? I’ll have to investigate his cello concertos some day. In the meanwhile, your chance of hearing Popper NOT at the cello is provided by the members of the New Trombone Collective playing his Requiem (originally) for three cellos and piano (or orchestra) on Etcetera KTC 1284, part of the 3-CD set KTC 1355. But, in that guise, not a very significant piece. I wonder what it sounds like played as originally intended, by three cellos and orchestra.