On Murmur you can unload everything you've got as he'll mainly hit the one in melee anyway. He can't move and if you can keep someone in melee then he only does the knockback/silence thing which doesn't hit very hard anyway.
I always use VT, even on trash mobs, with a decent tank you don't draw aggro; while I mainly use Mindblast & SW:Death as a finishing combo. Something which works very well, but makes your threat go through the roof (not a problem on Murmur, but it is on others mobs/bosses) is SW:Death followed by a Mindblast, with VE up you already get most health back from just the Mindblast, follow with 2 Mindflays and you're at full health again for a new cycle.
Did Shadow Labyrinth yesterday easy with a regular group on Thunderhorn (protection warrior, feral druid, frost mage, holy/protection pally & me, shadowpriest) and it was easy, wiped once on Vorpil (third boss), but the rest was really easy. On Murmur we had the druid + pally healing with the mage & me on dps. I did throw a shield on the tank after every Sonic Boom though while I moved back into position (givf longer range on Mindflay!). I love the versatility of hybrids in the 5-man instances and a pally main healer with shadowpriest backup is awesome, as long as the shadowpriest is doing dps the pally won't run out of mana.