Noumenality and Plurality

Schopenhauer's assertions, in #23 of World as Will and Representation, that plurality is "possible only through" space and time, and that the noumenal realm is "free from plurality", implicitly challenge Kant's attribution of plurality to that realm, e. g. his Kingdom of Ends, and his a priori distinction between duties to self and duties to others.  Nevertheless, Schopenhauer attributes to his own concept of noumenal Will "a variance to itself" (#27), and differences of "degree of manifestation" (#21), a multiplicity that somehow is "foreign to plurality" (#25).  So, his challenge to Kant in this respect is not without its own complications.  Now, the problem for both is to reconcile three theses that each accepts: 1. The noumenal realm is the ground of phenomena; 2. The noumenal realm is independent of phenomena; and 3. The phenomenal realm is plural.  Accordingly, one solution to the problem is a concept of the noumenal realm as essentially and exhaustively consisting in the generation of phenomena, e. g. the identity of the Will-to-Live and the Principle of Individuation, in Schopenhauer's system.  However, that solution is untenable in both systems, which, alike, assert an absolute heterogeneity of the two realms that is the basis of the Moral doctrines of each.  Instead, each leaves unexplained the positing of distinctions where discernibility has presumably been precluded.