The levels viewer is where the ONML levels are in Lemmix.
... ummm, you do realise there's a dedicated ONML Lemmix player just like there is for Original, right? Are you playing them through the editor or something? (And IIRC, even that has sound, just not music...) If you're using the player and getting no sound and/or music, you might've turned it off by accident - first make sure the option on the title screen is correctly set, and if it is, (during gameplay) use S and M respectively to toggle sound and music on and off. Those shortcuts aren't unique to ccexplore's versions, they've been there since EricLang's original code and are in every Lemmix-based game that I'm aware of (LPDOS/LPII included).
The versions on EricLang's website are out of date (they don't contain ccexplore's improvements), here's a link to the up-to-date versions:
http://www.mediafire.com/download/rurzngd7294fc87/Lemmix.zip(Orig and OhNo only, there isn't one for H93. I should really compile H93 from ccexplore's source - there again, I may as well just make the changes needed to make it H94 instead.)