> Have you ever had trouble playing two different dynamics at the same time?
I work about every day to this aspect of piano technique, IMHO fundamental.
Different dynamics in the 2 hands, ok.
But more difficult, and useful at the same level, is the technique to play simultaneously two keys or chords with one note in (strong or weak) evidence with the same hand.
One must be able to distribute the weight not only with equal quantity to all keys of a chord.
Listen to my Chopin op.48/1 or better Liszt-Schubert Litanei .....
To practise with this important technique there are dedicated excercises on Dohnanyi and other
books (also in the Brahms 51 excercises), or "by-yourself", play a chord and then repeat it playing
with evidence each note of it ( an arpeggio "internal" to this chord. Useful to repeat the other notes
of the chord holding the note in evidence).