One awesome sub (the EP500) is better than two smaller subs. It will go deeper flatter than the two smaller ones and still give you plenty of SPLs.
I'm guessing the only advantage to the two smaller subs would be the ability to place them in two different spots in the room and achieve more uniform coverage, but setting them up would be a pain in the ass.
Two EP350s would be interesting, but would only be necessary if one couldn't do the job, right?