On "dead cities . . ." it sounds as if M83 uses a lot of 80s synth gear. My guess would be Roland stuff like the Juno (it may even be an alpha Juno). All the drums on that album are obviously programmed and they sound like some kind of mid 80s machine (roland 505, 606, 707 i'm betting). Dunno where the synth string sounds come from, but it's probably from something cheap and cheesy.
If i had to guess, I'd say that, besides the drum machines, a lot of it was probably tracked live and direct. There are really "quantized" sounding parts that I'm sure are sequenced, tho.
Delays are really important for this type of music to get that washy, echoey sound. Lots of effects on the vocals (and then bury them in the mix). A vocoder would be good.
For the fuzzed out guitar, you probably wouldn't have to worry about getting an ultra natural amp sound -- you could get away with using an amp simulator. Then drench it in hall reverbs and delays.