We have a setup which involves an E5660 with 3 Disk Enclosures (DE6600). This array has come with the latest controller firmware (08.40.10.01), NVSRAM firmware (N5600-840834-D03) and ESM firmware (039F).
However on cross-checking with IMT in order to run with the existing infrastructure we are looking at the latest compatible SANtricity OS version being 8.25.X (preferable) or 8.30. I have been searching with no luck in E-Series manuals for a supported downgrade procedure.
If anyone is aware of this process or has a link to the same appreciate if it could shared here.