Kudos to gnoBoot and Trantor for the excellent work they did !!!
I installed gnoBoot alpha 10.4 with DSM 5, and managed to get it work. Thanks to the additional drivers I have a RTL8169 card working, a bluetooth dongle as well as a Huawei 3G dongle for Asterisk.
There was one thing weird though, during installation, after reboot, I got a few times that Synology Assistant had a time out and was not able to end the final step in which the configuration files were written.
When I logged in on xpenology itself (using gnoBoot's login screen of the NAS itself) and then logged out, for some weird reason, the system was capable of finishing successfully the writing of the configuration files. I don't know why or if I did something wrong, but I'm happy I got it working .