I don't know why ESPN says it will work, but here's my reasoning on why it shouldn't work:
Big Baby: $3,000,004 (yeah, three million and a happy meal)
Daniels: $2,388,000
Bradley: $1,418,160
Total: $6,806,164
Garcia: $5,500,000
Landry: $3,000,000 (No happy meal, sorry Carl!)
Head: $992,680 (although due to the whole league-pays-part-of-minimum-salaried-vets rule, the Kings only owe $854,389)
Total: $9,492,680 (or $9,354,389 if Head is treated at the lower salary for trade purposes, though I think not)
The Celtics are over the cap, so they can only take 125% + 100,000 over what they send out. That comes up to $8,607,705 maximum returning salary. There's no way to cleverly split it up to make it better, either. The Celtics don't have a TPE. I can't see any way to do it without either not including Head or bringing another minimum salary back to the Kings.