First of all, while it says Mastered for iTunes I am seeing nothing about a remix anywhere. As far as I know Death Magnetic has always been "Mastered for iTunes" on iTunes.
Second, nothing indicates this is a new release of the album. It says released in 2008, the description says nothing about it being new or remixed, and all of the reviews are from 2008.
Thirdly, and the final nail in the coffin (
)...the previews sound almost identical to the CD master anyway. There's maybe some slight EQ differences, the low end is a bit more pronounced for example, but it's the same dynamically.