you need:
– a 8spd right shifter. Doesn't need to flat-bar specific – any mtb shifter will work with any road mech, of the same speed (LX, XT etc.)
– a flat bar left shifter (SL-R440) OR and mtb left shifter. The SL-R440 is better, as it has less cable pull so is snappier and easier to set up, but you can get the mtb shifter to work using the limit screws (click 3 = big ring, click 2 = small ring, then use the low limit screw to stop it overshifting when you drop onto the small ring)
– cantilever/BMX brake levers. Not V brake levers, as they pull to much cable.
– a flat/riser bar and bar ends, if you like, and grips, obviously. I wouldn't go much wider than 50cm though.
Some people like drops, some don't. That's just the way it is.