I've been following a couple of facebook groups devoted to turbocider.
There's a lot of people using ingredients that have sorbates or sulphites or both, as an adjunct or even the main juice.
Some say they have to be boiled off, some say you just need more yeast.
It's... "interesting"
Now, I've checked wiki and found the temperatures required for decomposition of sod met and pot sorb are way higher than a simple boil would achieve - though perhaps it would have some minor effect.
Personally I stick to stuff without sorbates and sulphites, but I'd love to hear from anybody who actually knows either chemistry or is an expert on how yeast gets on in hostile environments