Well...
Deathbringer MH vs Crul'Shorukh MH
DB is 6.4 dps lower but 19 higher average damage for your overpower and WW.
Crul has +36 AP which means it's 8.7 higher DPS on white attacks and 14 lower damage on overpower/WW. It's also 16 higher damage on your bloodthirst.
Since white damage and BT make up the bulk of your damage and overpower/WW is a fairly small portion, Crul is probably better. It comes down to the weapon proc on DB.
Deathbringer OH vs Doom's Edge OH
DB is 3dps higher (because OH damage reduction) but Doom's edge has .8% crit and 18 AP.
Again, aside from the proc on DB, doom's edge is certainly better so it comes down to the proc rate.
I'm pretty sure Crul + Doom's Edge is better. Try using the Recap addon with Deathbringer x2 and see what percentage of your damage is coming from the weapon proc, should give you a better idea.
Either way, keep the Deathbringerx2 if you have it, put life stealing on them and swap when ever a mob (or chromag) in BWL is vulnerable to shadow