For now, yeah, they're only in the box set. And Rhino's site
doesn't say anything about individual album releases. But the box-set review on AllMusic
claims that the individual albums are "tentatively scheduled to follow, three to four months after this set's…release", so maybe their reviewer knows something I don't.
There are some nice little details in the remastering; you can hear the attack on picked guitars and on snare drums more clearly, and you can hear the beginning of the acoustic guitar part at the start of "Burning Down the House", where the old CD faded it up in mid-phrase.
And I've listened to a couple of the 5.1-channel remixes now; so far, they're interesting without being essential. Nothing too pan-crazed; instruments mostly spread across the front three speakers, ambience and some percussion and a few keyboard bits thrown into the rears. I don't think they'll replace the stereo mixes, but they're kinda cool as supplements.
As far as Remain in Light
goes, since I know it's your favourite: the CD side features four unfinished tracks from the album sessions (one of which, "Right Start", is clearly an early prototype of "Once in a Lifetime"). These are interesting rather than great, IMO, but they offer some cool context: it's amazing to think that the insanely-tight final album came out of this sort of loose demo material. And the DVD side has live video clips of two songs taken from the Remain in Light
tour, with Adrian Belew and Busta Jones. Very nice.