Knowing the instruments you're writing for isn't always possible. For that reason, I do believe that, as a composer, I need to talk a try ideas and different drafts with instrumentalists.
Today, I have been with Jordan Murray, a percussionist and a student of Guildhall School of Music and Drama, who helped me with some particularities of the marimba.
I showed him my first draft and it had some issues:
1.- All chords are possible if they appear separately and with time to prepare. The percussionist must have enough time to adjust the opening of the mallets in each hands.
2.- If I write fast motifs, I must consider two voices instead than four. For example, in my first draft I had quintuplets in four different voices which are doable but with enough time to prepare the opening of the mallets.
3.- If I want kind of similar movement with four voices I must consider parallel movements to the same direction (image 2) or parallel movements to different directions.
4.- Eventually, I can keep, for similar gestures, the same opening of the mallets, for example if I have a 9th interval I must have no less than a 7th (for example for a quintuplet = 0, 9, 9, 7, 8)