again, this is one of those things they've never bothered to clear up!O.o
i'd say though, go with the similar line that was used in the codex: daemonhunter hunter Q&A regarding psycannons & incinerators being one-handed or two-haned: "look at the models!" they're obviously two-handed!
so, as the models themselves are modeled as two-handed, i would say then that sonic blasters and blastmasters are both two-handed weapons!
as an aside, the doom siren rules were (yet again!) misprinted in the 4th printing... you are to use the rules as printed in the 3rd printing as they are the right ones! (fools can't do anything right!
)
cheers!