I know it has its own thread, but this 26-disc monster is worth documenting as a Megabox. King Crimson / 1969 box set | superdeluxeedition
Even if he suddenly retired and a “Complete Robert Pollard” box set was released today, it would be 100+ discs....
Well, I’m now the proud owner of the 222-CD Bach 333 set of J. S. Bach’s complete works. See you guys in a few years. Two hundred and eighty hours of music. Holy moly.
19 CDs of Shakin’ Stevens: Shakin’ Stevens / Fire in the Blood: The Definitive Collection | superdeluxeedition
Not a box set pre-se (or, eight such), but each Wedding Present album (eight of them) has a 3CD + DVD edition, so that's 32 discs...
The biggest box in terms of discs I have is the Wishbone Ash Vintage Years set at 30 CDs. However, I have a bunch of Rolling Stones sets that are even bigger in terms of "box size": the biggest offender is the Grrrr Deluxe edition - there may be only 5 CDs and a 45 in there but due to the poster and oversize book the box is enormous! Similarly the box for the Brussels affair is huge too: there's only 3 LPs, 2CDs a poster, a velvet sack and and a book - and a watch in there.... It even has its own shipping box! ....which was delivered in an outer box, as I remember.
It could be worse, try this complete on 7" 45 RPM discs (and some Classical into the 1950's was issued in that form, mainly short pieces).
Al Stewart / The Admiralty Lights: Complete Studio, Live and Rare 1964-2009 – SuperDeluxeEdition “Comprising 50 discs, this astounding set follows the legendary singer-songwriter from humble beginnings in 1964, to global stardom in the ‘70s, through to his most recent recordings in 2009.” Fifty discs definitely qualifies as a MegaBox.
Horslips / More Than You Can Chew 35-disc box set – SuperDeluxeEdition SIGNED by all five band members• 33CD+2DVD box set • 200-page book • Limited to 1750 units • Over 250 previously unreleased tracks
Camel / Air Born: The MCA & Decca Years 1973-1984 – SuperDeluxeEdition Anyone for 32 discs of Camel?!