I'd probably go for demolishers if you want strong blasts. And they're a good place to get posession.
Haven't considered an infiltrating firebase of sonic blasters, to be honest. How does it work? I'm often running infiltrating 20-strong mellee-oriented slaaneshits with meltas (regular guyz with
MoS and IoE) together with Cypher. And they're very effective. Shrowded +
fnp makes the squad unexpectedly resilient. Small arms need to go through 3+/5+++ - and that's almost as durable as 2+ while big gunz still have to go through cover. And there are not much ap3 or better weapons that ignore cover. Even so, they're generally blasts, so won't kill more than ~4 guyz as you can always spread out. And H&R proves very useful too.
Oh...and the enemy can't sweep us. Cypher has
ATSKNF 
The only problem is that they're not fearless => can sometimes fail ld10 and run/get pinned. But not that it happens too often. On the other hand, they guyz will rock 2+ cover and
fnp when they g2g in cover.