Set pieces? Quite possible Boro would have been working on a new one for this game.
I imagine knowledge of set pieces and strategies taken by which players would be a very decent advantage.
As would the key factor of knowing if we were playing a 5 man (3 CB) defence or a 4 man (2 CB) as they tend to have different strengths. For example against yourselves we got it wrong IMHO by playing a 4 man defence, (with Ayling part of the 4 as well when he's much more effective in a 5.)
With a 4 man defence we can then overload the midfield and dominate that area of play. The solution to that for opponents of ours is to then put more emphasis on pinging long balls to bigger target men further ahead, making the most of quick play down the wings when this isn't an option, to effectively take the midfield out of the equation wherever possible which you did against us, without spying may I add. Their defence then compacts into the centre to create a denser wall of players facing where most of our attacks will come from.
If we play a 5 man defence then this is obviously more solid, but especially in Hackney's absence, we lose a little of our well known strength in midfield. Our opponents then know that it isn't a complete "no go zone" through the centre as much as it was previously. In terms of our attacks, opponents also know to dispatch their best ball-winning and tackling players down the flanks as the likes of Bangura and Silvera can break with speed down these and are more likely to get utilised.
Of course a lot more advantage would be gained if knowing how fit Hackney was to play in advance, or whether we had other injuries that had flared up (such as Bangura as mentioend), how likely Casteldine was to start instead of Gilbert if not as the two require different marking strategies, etc.
Lastly, a little advantage could also be gained if penalties were seen being taken and more importantly the identities of any players other than Tommy Conway tending to take them, though I think this strategy would have been more prevalent before the second leg for obvious reasons.