@minute have you considered shipping the kernel with CONFIG_PREEMPT_DYNAMIC=y? That would allow setting preempt=none|voluntary|full on the kernel command line for more (or less) realtime-oriented setups as required.
The new A311D is very pleasant to use and it can almost do live realtime audio (with a multitrack synthy project) at audio buffer sizes above 256, so I’m trying to tune the system a bit further to see if’s possible to make it run with 256 or 128-sample sized buffers.
Alternatively, what’s the current recommended way of building a kernel with a custom config and installing it to the SD card? Is reform-debian-packages/linux a good place to start?