You could also see if there is a threaded male/pex (probably 3/4) that you could thread into the tank and then a pex on the other side of the fitting... I just bought fitting for a laundry tub sink that went directly from female threads to pex...even swiveled. That is if you have enough play in your pex to reach that far...
http://www.supply.com/shop?nid=48868...FZGIaQodcQcHyQ
Something like this..Menards or Home Depot probably carries them. On the cold water side i wouldn't worry about anything..on the hot side i'm not sure if they want pex coming right out of the tank like that.