Well, you landed on exactly why I absolutely love both of the wrasses we're discussing here. 5 days is till fairly new and I'd bet the 6 line will settle down, some. They're always bullies but the yellow coris will eventually establish a home base in the tank figure out how the best get away from the 6 line when required. There should be plenty of room in a 125g tank for both to figure it out. Worse case, trap the 6 line and give him a time out is a separate tank for a week or two. This can have the effect of adding the 6 line after the yellow coris. Sounds to me like your goal it to keep both of these two fish and I think a little time will help reach that goal.
Side note: Make sure you have a good lid. Both of these species are world renowned carpet surfers and when one of them is new, the risk is even higher.
