I'll second, In Principio. Your list are certainly at the top of my own that I would have otherwise recommended. I'd add, Arbos, and Orient Occident. There is a compilation that you might also enjoy that includes Part as one of the artists. It is on Nonesuch (I think it was also on ECM for a while) and called, Silencio.
Another composer you might like, going a bit further in the realm of minimalist modern... You might try John Adams, On the Transmigration of Souls
More conventional and yet I might also recommend in association with the Part you mention... Henryk Gorecki: Symphony 3 "Sorrowful Songs"
Another composer you might like, going a bit further in the realm of minimalist modern... You might try John Adams, On the Transmigration of Souls
More conventional and yet I might also recommend in association with the Part you mention... Henryk Gorecki: Symphony 3 "Sorrowful Songs"