You can tell the OS by booting it up, going into the MASTER -> SPECIAL Menu and scroll all the way up. Then it displays the OS Version.
Regarding the upgrades, here are a few buzz words, which you can look for on this forum, on the www in general and in some really active facebook groups as these have been discussed several times:
SCSI Upgrade (if necessary:
http://eiiiforum.com/index.php?topic=3793.0), SCSI2SD v6, new sliders, new OLED, check 5v rail on the Power Supply, recap or replace entirely if you have a bad feeling about it, reseat and clean the IC if you want to to be 100% sure.
Have a look at these files and links which are a good start for your questions:
https://www.cyborgstudio.com/e-mu-emax-sehttps://www.gearslutz.com/board/attachments/electronic-music-instruments-and-electronic-music-production/535191d1456158457-emu-emax-hd-se-scsi-htx-upgrade-question-instructions-scsi2sd-emax-.pdfhttps://www.youtube.com/watch?v=3YPNt83o0Pohttps://www.youtube.com/watch?v=a3Vc3SdZJ2Yhttp://www.emxp.net/Good luck!