Install Saiy assistant app from the Play Store.
Choose Saiy as your voice assistant.
Thoroughly configure Saiy to your liking.
Disable the pre-installed voice assistant.
Thereafter, pressing the silver button activates Saiy with the cover open or closed.
Saiy works very well thus far in my few weeks using it.
Cheers.
So, it appears that the silver button launches 'Voice Search' rather than 'Assistant'. Voice search doesn't seem to be as capable as Assistant (I think it may just do a Goole Now search). Anyone got any ideas on how to change this behavior?