Dividing classical into programme and absolute music is slightly problematic, and I don't think that either half of the divide explicitly refers to ambiance. A third category was proposed by Franz Liszt:
Liszt's own point of view regarding programme music can for the time of his youth be taken from the preface of the Album d'un voyageur (1837). According to this, a landscape could evoke a certain kind of mood. Since a piece of music could also evoke a mood, a mysterious resemblance with the landscape could be imagined. In this sense the music would not paint the landscape, but it would match the landscape in a third category, the mood.
Also, how about musical Impressionism? Debussy can be ambient, though I'm not so sure about Ravel. Is there anyone else from that period who seemed to compose ambient music? There's Satie -- a direct influence on Budd and Eno -- but until the early Eno albums, there doesn't seem to be much else. During the 20th century, art music fractured into dozens of frivolous experimental movements, all seemingly dead ends, so how a "popular" music artist involved in glam, of all things, managed to pick up where Satie and Debussy left off fascinates me. It seems like there should be a missing link somewhere along the way.