What rabbit-hole did you fall down today, Thad?
Well, first of all, Rob Beschizza at BoingBoing posted a link to an article titled Color Coded: Panthro, over at Color, where Monique Jones discusses the racial coding of Panthro -- why we think of him as a black guy even though he's a blue-gray cat person. Obviously Earle Hyman's mellifluous baritone does a lot of the heavy lifting, but it's not just that; it's the character design, too -- he's a different, darker color than all the other Thundercats, his features are wider, and his head's shaved.
Anyway, Beschizza's post had this at the bottom:
And I thought hey, that's a pretty good, clean rip of the extended version of Panthro's theme song; somebody must have worked hard splicing that together, and I wonder if there are any more.
I found a few others from the same poster, and by the time I got to this one
it became clear that okay, these are definitely not fan edits, they're original recordings from somewhere.
So then I found a video called Thundercats: The Official Soundtrack (linked because embedding is disabled). It's a 2008 call to action petitioning WB to release a soundtrack album, and it's got samples of a bunch of different tunes "cut from the original master tracks" to demonstrate that they're out there and all WB has to do is publish them.
So what I'd heard in those YouTube videos were, presumably, copies of those original tracks.
I poked around the Internet a bit; there's a thread on FF Shrine that links an incomplete set of the songs (plus some other stuff of questionable provenance) and discusses them in detail.
So yeah, I have a new #2 Unpublished Thundercats Thing I Want Most. (#1 is Lynne Lipton's personal videos of the recording sessions.)
Also, somebody made this fan video:
Presumably the new theme song is from the 2011 soundtrack album.
It conks out a little bit at the end, but the first 2/3 or so does a decent job of reconstruction the original intro with material from the new series.