Wow, that's the best reason ever to ignore the special rules printed in a Codex!
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Bonus to reserves rolls from different special rules always stack, but don't always work in multiples of the same rule.
Just to recap:
Doesn't stack in multiples
Astropaths: As long as an Astropath is on the table, you add +1.
Lictors: As long as a Lictor is on the table, you add +1.
Does stack in multiples
Autarchs: As long as the Autarch is alive, you may choose to add +1 to reserves this turn.
Hive Tyrants: As long as the Hive Tyrant is alive, you add +1.
Swarmlords: As long as the Swarmlord is alive, you add +1.
Doesn't work at all, RAW
Deathleaper: As long as Deathleaper is on the table, you add +0 if no actual Lictors are on the table (until FAQ'd)
Guard would have the best chance with Autocannon teams using "bring it down."
Duke
Well, autocannons do work pretty well due to their rate of fire and how cheap they are, but I'd still prefer ML and HKMs. If I played guard.
For Tau, a Skyray or two, plus a bunch of markerlights in other units would work pretty well. Really well, in fact. A pair of Skyrays and enough other markerlights could kill 3-4 Carnifexes/Hive Tyrants quickly. Ion Cannons would work well, too.
I am the Hammer. I am the right hand of my Emperor. I am the tip of His spear, I am the gauntlet about His fist. I am the woes of daemonkind. I am the Hammer.