The Musikos Sports 2 CD has finally surfaced, and—thanks to Retromatic posting it on librarymusicthemes—two more NFL Primetime tracks from 1988 have been identified. Unknown Song #7 is "Play Ball!" and Unknown Song #16 is "Grid Iron Great." Oddly enough, neither of these were among the samples on the Musikos promo disc I mentioned a while back. Musikos's albums do not have artist credits for any of their songs, so it's not presently clear which composer is responsible for either piece. According to info posted by Godzfire, there are four known composers attached to Musikos: Neal Davenport, William Soden, Steve Diamond (Dimond?), and Jamie Hoover. Play Ball! could probably be any of those four, but Grid Iron Great really doesn't sound like Soden's work.
The question as to how ESPN acquired these Musikos songs hasn't been solved yet, either. NFL Primetime was using them in 1988, but these Musikos CDs weren't released until the early '90s. Either John Colby directly licensed them from their composer(s), or there's some mystery music library out there that's even more obscure than Musikos.
Special thanks to Retromatic for acquiring & posting Sports 2, and to Godzfire for informing me that Retromatic had obtained it.