(SPOILER)
-Mission to Deep Space. It actually sounds a lot different this time around. I do like it though, and it definitely goes with the rest of the game's music (Which I also really enjoyed.)
-As for the optional bosses, I've really only run into two so far, and one was Gabriel Celesta. The other was Dirna Hamilton. She's from that sidequest on Gemnity in the battle arena in Star Ocean 3 I believe. I'm sure you'd probably remember better than I would. :-)
And Iseria was listed in the credits, as Iseria and not Ethereal strangely enough.
I'll update on the other bosses as I go through the gate.
And while that cover art is nice, the Artifact Box came with a different one to replace it with, which I thought looked nicer. I hope they choose the alternate one for the English release.