Which openings are playable at (pre-)FM level - IM level? Which defenses against 1. e4 and 1. d4 should a 2250-2300 FIDE player use to become an International Master, if he is: 


Aggressive-minded
Tactically proficient
Keen on dynamics
Original/imaginative/offbeat but still positionally prudent


I mean, there are so many allegedly "playable"  openings but many of them have minus positional sides (Benoni, Benko, Budapest, Tarrasch etc).  What does Kasparov mean when he says that all reasonable (sound?) openings are playable? 

What does his "reasonable" really mean? All over the internet, you find advice for all players except for players above 2200 FIDE ELO. It is assumed these players all know what they should do, but this is not the case I think.

There are books on opening selection (Giddins, Yermolinsky, Hans Bo Larsen, Dvoretsky, for instance), but they are too general.

So, to summarize, which openings are sound with black against 1.e4 and 1.d4, taking into account my stylistic preferences?
Opening advantages are fine things. Maybe you can even find an opening that lends itself to your 'style' of play. But what value does any of this have? Really?

Firstly, to become a master you must be able to play all sorts of positions well. Playing a limited set of openings directly contradicts the goal of practicing a wide variety of positions. Or does it? Really? You see, we're not masters yet, so our games are likely to be unpredictable and messy.

What this means is that until your middlegame and endgame skill is at the master level your opening choices matter very little. Think of it the other way; if you're playing a master and you've somehow managed an opening advantage the master will just dig in and outplay you in the middlegame or endgame. To become a master, you will also need to acquire these skills - so you'd better find ways to get opening-disadvantages as much as possible!

I guest the real point is that even heavily unbalanced positions often have excellent drawing chances for the disadvantaged player. A master will be able to make use of these to greatly reduce the chances of a loss. The difference in opening choices in this sense comes down to the master's goals for a particular game. Would they be happy with a draw? How much do they want to risk pushing for a win if complications might also favour their opponent? Perhaps they check a database and find that their opponent only wins 2% of games that feature a Queen-side attack when the dark-square Bishop is exchanged - interesting, maybe it's worth trying a Trompovsky as White and pushing c4 early?

This line of reasoning is just beyond being useful for non-master players.

So now we see what Kasparov means when he says that all openings are playable. In almost all cases openings are simply irrelevant. Masters might try to expose each other's weaknesses with them but even at the highest level, it is middlegame and endgame skills that decide games.