I've done it!
After a week of trying, a 32 gb sd lost by formatting errors and a lot of stress from inexperienced linux...thanks seaniko7!!!!
For the black pearl the problem is, in my opinion, that the installation of Obuntu should be done from a firmware Booxtor, NOT from original firmware. I solved by first installing the utility of seaniko7 to unlock the M92, then installing the latest firmware Booxtor and finally following the whole procedure for Obuntu.
I propose me as a tester for the applications of music notation that will surely be using a lot, being a pianist-composer. Many thanks to Seaniko7, to Booxtor and all the users who make possible these improvements!
PS: as you can see the status of the battery?