Aussault Cannons are mounted. Unless your Kill-Team is rolling in Terminator Armor, they shouldn't be allowed to use one. Also, I don't know what the loadout of your Storm Shield carrying Marines is, but if they're walking around with heavy weapons as well, keep in mind that's against RAW. Heavy weapons require two hands to use.
Remember that Force Dome doesn't stop melee attacks, so the key is having enemies close the distance with the Librarian quickly and force him into melee if the Multi-Melta is jacking your bad guys up. I also have no idea why you consider Blood Frenzy overpowered. It's a nice ability no doubt, but it doesn't last very long and I never considered it broken.
While there are certainly some balance problems inherent in any high-power game such as Deathwatch, D&D, Pathfinder, Exalted, etc., it helps to check up on some of the things your group is doing to ensure that it complies with the rules. DW is actually much better balanced than D&D is at higher levels, and Exalted starts off at broken, and gets absolutely ludicrous. I'll take Deathwatch any day.
)...I assume that all of us here are, more or less, role-players who understand that we're all making a cool adventure story together, for our own personal enjoyment...(As GM, the only real surprises i get are the players' hare-brained idears and their bloody vile luck....and i appreciate all of it; it makes my day!)