The problem is on task manager every gpu comes up as being used at 0% apart from GPU 0 which uses anyway between 1-7%
Unless you looking at compute load (in task manager) you won't see anything when mining.
Which algo/miner software are you using? Did you check usage in other utilities (gpuz, hwinfo, even afterburner)?
So from 6 1080ti's overclocked the daily estimated sits at around 12USD which quite frankly doesnt seem correct
Again, without info on what coin you are mining no estimate can be drawn.