[@Conscripts]

Well if it were me, I would start off by having your ranged cavalry engage the enemy in a Cantabrian circle fashion.  
Then use the 300 Darkforest Ranger's missile support when they get close enough, firing their bows in such a manner that the arrows start to fall from pretty much right above the enemy.  As they raise their shields, if they don't do a testudo, have the whole crossbowman force fire their volley.  After a few little bits of this launch an infantry assault on them while at the same time having the cavalry as a whole pierce through one of the flanks, envelop around the enemy, and crush their backlines/missile troops.