Hi!
The enclosure recognises them as being monarch and auxiliary, in not partnered configuration.
As this BL890 is coming from second hand market, it was missing the documentation.
I managed to find a document named "HP Integrity BL860c i2, BL870c i2, & BL890c i2 Server Blade Installation Guide" which I should use for setting it up properly.
It seems indeed I have to inser one at time, and let them get an IP address, then insert the other, and only when completed insert the front backplane.
Unfortunately, my holiday spare time finished and I'll have to go back to my real job in software development.
I'll come back to hardware playtime later on in september
Thanks for interest in my troubles! :)
I'll keep the group posted!
Cheers
Gianluca