Name suggestions: I think the best way to go is something related to how they are "first" that fits with V-Moda's overall image.
Primus (Latin for "first")
Primus Inter Pares ("first among equals", phrase used to indicate something that is formally equal to its peers but looked upon as having special importance-obviously fitting considering the M-100 PPU are technically equal to the production models but have special importance since they are first and limited)
Janus (Roman god of beginnings)
Principium (Latin for "beginning")
I find the above fitting since part of V-Moda's motto is "Inspired in Italy", and I noticed on the FB page that a lot of pictures of V-Moda headphones are taken of them on busts (along with plenty of Italian imagery on the V-Moda website).
The other way to go would be something generic and professional (that again focuses on how they are first):
V-Moda M-100 I.R (initial release)
V-Moda M-100 R. (release spec)
V-Moda M-100 Limited Edition
V-Moda M-100 V-nitial (a play on Initial of course, while sticking with the V emphasis)
My personal choice:
V-Moda M-100 V-nitial
The V would be a unique design: the left part of the V would be upright like an I, so that no one would miss the fact that it's a play on the word initial. Basically something like what the V looks like on the Cadillac-V logo (minus the flags to the right of the V, of course):
I like it because it's simple and creative at the same time without being childish, because all it is is indicating that they are the first versions of the headphones available. Obviously the V wouldn't completely copy the shape of the V in the Cadillac logo, but it would be something to that effect. Finally, I think the phrase "Primus inter pares" should be included somewhere on or in the packaging of the PPU units since the phrase is so fitting to the PPU units and since the use of Latin is so fitting with V-Moda in general. Hell, even if Val just signs that phrase on the card that comes in the box.