Thank you. On my Sinology Ds216j i used armv7 (as i supposed). It works and i can extract rar5 archives. I'm doing some tests.

Same file archived rar and rar5:
with original 7zip it only extract rar (rar5 shows error as you already know)

with this 7zip you gave me it extract both archives.

Speed extraction seems the same, but i tried with a very little archive (100mb). As soon as i download large archive i'll test speed extraction with old and new 7zip.
Maybe it's just a bit faster with new one version.