Sara, that is (as usual) a most fabulously-written and fabulously-listened response to the piece. You have a way of getting at the nub of things which I admire (and am rather jealous of!)
As you both know, I am a enormous admirer of Stevenson and his music (and his pianism too), and I'm so pleased if my mentioning the Passacaglia somewhere or other was some factor in introducing you both to the piece. It is an absolutely awesome work, and as Sara says, no need to apologise for saying so, or to hedge one's language - it's one of the great piano works of the last century, no doubt at all about it. As you both hint, it is partly the way in which it deals with these unprecedented questions of scale and form and virtuosity which contribute to this - the unflagging invention and the unflagging energy (of performer too - and isn't the man himself just
the most fabulous pianist!?). But the compositional technique is staggering too - that triple fugue on the Dies Irae, BACH and Stevenson's own subject, all over the DSCH ground bass itself is just one, incredible example. There's a great humanity in this piece, as in all of his music, too. This is one point of contact with the Rzewski variations The People United Will Never be Defeated which I think Sara was hinting at. This democratisation which allows tonal elements and much more ambiguous elements to coexist without the slightest contradiction. In the Rzewski there are recurrent figurations which are functionally atonal although built out of tonal cells, transposed through the keys to produce a kaleidoscopic harmonic effect. Stevenson does something similar, often - there are, in the opening pages, for instance, cascading minor triads which slip chromatically through the keys in a very similar way. It's partly this kind of writing which gives both pieces that special feeling of rigour and logic being tempered with sensuous, approachable beauty. It would be interesting to make a more detailed and extended comparison...
I love the man and his music; my knowledge is limited, though, to the Passacaglia, the Busoni/Faust Prelude, Fugue and Fantasy, the Fantasy on Peter Grimes, the two piano concerti, the songs on the beautiful Delphian disc and two or three other CDs of the piano music. I also play or play through (to the best of my ability) the first three of those pieces at the piano. Far from ideally, I should emphasize, but as always having a working relationship with the music increases one's admiration a hundredfold. There's also the Toccata symposium on Stevenson which is, I think, the best introduction to the composer and his very individual world.
A great and too-little-known figure who deserves lots of listeners. Anyone interested in Busoni, Liszt, Alkan, Sorabji, Grainger, etc. etc. will find him a very rewarding composer to explore. May the thread flourish!!