Hey, I'm new to this forum, I found it via a google search for people using the Yam monitors with the sub. I have had the HS50Ms for a while now and just got a HS10W sub.
The reason I was searching was I wanted to see where people have their high & low cuts, and eq switches, etc set. Obviously, stuff will vary by room and taste, but there has got to be a best practice, and most people probably don't have this set up in a huge room, so what sounds best is probably similar.
I do agree with Josh though, you probably don't need the sub for mixing metal with the HS80s, but if you are mixing music that has a focus on the sub bass, especially sustained sub bass, like say modern EDM like dubstep or drum and bass, then it would be crucial, because you are trying to push the subs in a club with your track and you need to be able to translate to that.