Towards the end there are several culminating moments with these superchords, arpeggios, aleatoric passages, and a four chord progression played fortissimo by the brass section in measure 231.
If ever there was music that could stand in for my alter-ego/super-villain and his maniacal laughter -- this is it!
I never gave much thought to how you could "label" these triads, because honestly, I don't analyze my music that deeply when composing. Usually, I sketch out ideas, explore them, stretch them into new territory, and then analyze why I chose those paths much later. Also, I'm less concerned with the theoretical "function" of a chord and more about its sound and what other chords can be used before and after. (Yes, I consider voice leading, root progression, set theory, and all the other tools I've learned, but I'm not really a theorist -- I'm an artist, and in reality I let my ears lead first and then let my brain analyze why my ears chose those sounds!)
There are a lot of interesting ways to analyze this section. For example, you could note that the root progressions (Eb, A, F#, Eb) are all tri-tone and sixth relationships and that the top notes (Bb, G, C#, Bb) are also, with the result being intervallic mirroring! Or, I could point to the existing motifs and how they are all superimposed throughout the entire work and culminate in this moment! But, we are hear to talk about these four chords and their "labels" (wouldn't want my villainous monologue to get the best of me!)
And those four chords are (roughly) Eb(#9), F+9/A, F#m(maj7), and F#o7 with extensions b9, 11, b15, 17.
Here are the original four chords, as scored for brass with some doubling.
making it an Eb(#9) chord
it is F+9/A. You might argue that it is an A+7 with a #13, but does it really matter with whole tone collections ... no ...
When stacked as thirds, the bottom four are clearly F#o7, with the remaining four near the 9th, 11th, 15th, and 17th extensions. You might be saying, "But, 15ths and 17ths aren't really extensions..." and you might be right, I don't really know! (Mu-ha-ha-ha!)
The way its voiced originally makes it feel like a diminished chord (that melodramatic one!) and what's curious is that the F#o7 might want to resolve to G, but that G is already superimposed as a G7#9, so there's some wanting and having, bait and switch, villainous joyful cruelty to that chord...