We're playing Deathwatch adventures with high level Dark Heresy characters (works quite well). However, the horde combat rules suck in my opinion. Every creature becomes laughable when battling a horde of them, except in the instances where they randomly kill you outright.
Here's an idea for an alternative.
The GM keeps the following stats for a horde:
PCs Attacking a Horde
Horde Attacking PCs
Benefits of This Variant