i also think you should explore Scriabin post "Chopinesque" where he really started developing his own harmonic language and stretching tonality, in a way different from what the kids with the new/2nd Viennese school were doing i.e. Schoenberg etc....,
this piece is so deep. op 72 (1914) Vers la flamme
about it:
"...Alexander Scriabin completed his Vers la Flamme, Op. 72 for solo piano in 1914. It is a brief work around six minutes in duration, but its epic quality is pronounced and well contoured. In keeping with its title "Towards the Flame," the music careens from a somber, burbling opening to an ecstatic vision of a cosmic rupture.
Vers la Flamme is too good to be dismissed. It is through-composed, and progresses to an epiphany of vibrant pianistic color that is not revolutionary but stunningly approached. The intermediary music (the first three minutes) builds like an especially driven opening by Chopin, which is exciting and does not overstay itself. Its destination is an echo effect of repeated notes in the high register of the piano, becoming the new focus for listeners. This build is a continuous, supercharged, romantic texture. The echo effect in the piano is something modern and could not have been produced in the nineteenth century. It does not sound like a grafting of romantic and modern techniques. Scriabin no doubt was reaching for a mystical epiphany, and the sound of such. For alert, informed listeners, the beauty of this brief movement is its apparent clawing its way into a new style, with its roots in the old. The effect, in essence, is Post-romantic in the manner of Mahler's symphonies, intensely contracted...."
you also might want to listen to various Stravinsky works including his piano sonata.
there's lots of good 'non Russian' out there too but this is where the majority of my familiarity with post romantic/modern repertoire lies at the moment.