Thanks for the description! I was listening to this all week and thinking how odd it was that I wasn't hearing the usual Carter "dialogue" between instruments - it seemed more like "song without words", for lack of a better phrase. The groups are indeed really hard to pick out just by listening to it. Not sure if that's a problem with the music or just the limitations of recordings.
The oboe doesn't lend itself to the type of virtuosity associated with the strings, the piano or the clarinet. The purity of the notes,the sustain,the breath induced vibrato, and the long limbed melodic lines are more in evidence; a delightful work perhaps not as sublime as Maderna's compositions but worthy of performance. Not a whole lot of oboe concertos out there.
I heard a performance of this piece in Minneapolis some years ago; Heinz Holliger was the soloist there as well. I found the live performance had greater clarity of the instrumental lines, and I heard more going on than in the recording! (of course the recording is performed wonderfully, but the recording quality is unhappily somewhat lacking.)