... wheras version 3.0 ive read will ask for the serial number and authorize + run (im hoping)
I think, you're chasing ghosts. I mounted 3.01 update dmg and there's Syncrosoft License Control package inside it, which means that the licensing scheme is the same as in 3.1.
Quoting from Steinberg webpage:
The following chart shows serial numbers resp. installation codes that can be used for installing the according program versions.
Registration of the listed software requires a USB-eLicenser (USB dongle).
Version on media Serial Number resp. Installation Code
Cubase SX 3.0* BADPY-AAAZK-HGMOF-FFVMA-AOZNA
Cubase SX 2.x 1089237371
Cubase SX 1.x 113722821
Cubase SL 3.0* BADPZ-BAGDF-NHYCP-POABA-AHNYA
Cubase SL 2.x 1074587951
Cubase SL 1.x 085468983
Nuendo 3.0* BADQA-BAZAJ-LDYUI-UMWXA-CWDXA
Nuendo 2.x 1057475123
Nuendo 1.x 903235895
HALion 3.0* BBCCS-AAFUD-QDFGQ-TNRQA-AIZW
*Program versions on more recent CD/DVD releases (3.1 and newer) can be installed without serial numbers resp. installation codes.
EDIT. IMO, you'll be better off by running one of the Win versions of 3.1.1, that are floating around, in either emulation or on real machine and converting your Atari files there.