Unpitched percussion, filtering/selectiing/dynamics

I cannot filter an instrument of a drum kit, neither by stem direction nor by voice nor by pitch. I also cannot select several notes of a single instrument by left/right arrows. And also it is not possible for me to give snare and kick drum different dynamics.
Is this definitely not possible or do I just not know how to manage it? The only workaround for selecting single notes of a drum kit instrument seems to be to use marquee selection.

Have you tried displaying the kit(s) in a layout temporarily as single-line staves and adjusting dynamics from there? The dynamic markings will likely not transfer to display on the five-line staff when you switch back, but you may get playback more in line with what you want.

For information about how to change the presentation type of a percussion kit, see here.