At present Optio has well over a thousand army lists, and counting. I reckon to have something like 2000 armies to choose from when I'm done.
Well, I cheat.
Players put a lot of time and money into acquiring the armies they need for the rules they play, so I thought, why not just let them use those armies? The generic troop types are pretty much the same for each ruleset - a pike is a pike whether in DBA, l'Art de la Guerre or Triumph.
So I drew up a huge master table of Optio troop types (34 and counting) to which other rules' lists could be adapted. Optio troop types are as of writing:
SHOCK HEAVY CAVALRY
BARDED HEAVY CAVALRY
THESSALIAN CAVALRY
MEDIUM CAVALRY
ARCHER LIGHT HORSE
JAVELIN LIGHT HORSE
CATAPHRACT
KNIGHT
CAMEL
LIGHT CAMEL
SCYTHED CHARIOT
HEAVY CHARIOT
LIGHT CHARIOT
INDIAN ELEPHANT
AFRICAN ELEPHANT
PIKE
HOPLITE
HEAVY INFANTRY
CLUBMEN
ARCHER
PAVISE SPEARMAN
SPEARMAN
LEVY
SOLDURII
GAESATI
HEAVY WARBAND
LIGHT WARBAND
AUXILIA
PELTAST
SLINGER
INFANTRY SKIRMISHER
WAR WAGON
HEAVY ARTILLERY
LIGHT ARTILLERY
That covers pretty much everything in DBA, Triumph, ADLG and DBM(M) - with a bit extra. As I work through other lists I'll see if anything needs to be added.
No need to mention of course that the players will have to already possess those army lists. All I supply is conversion tables for the troop types. Deciding on points, army sizes, composition, etc. will depend entirely on the provisions of those rulesets. So you assemble a DBM army, put it on the gaming table, and play an Optio game with it. Simple as that.
Here is the DBA conversion table as an example (click on it to get a clearer image). Conversion tables will be offered for free and input from players will be invaluable. Nothing is written in stone.