[Nightwish]

I would muck this preflop. Your immediate odds suck, and even when the action was completed, you were still only getting 3.5:1. When you're playing a small pair like 66 multiway, you're mostly playing for set value, so do you think you're going to make another 4 BB postflop those times that you do flop a set? I don't think so. (Don't forget that there's also a small fraction of time that you'll lose even with your set.)

Also, what were you going to do if the turn hadn't been a 6? Please don't tell me you were going to fold.

On the river, it really depends on what the SB is like. There are players who will bet just about any pair on the river when a flush comes cause they think the scare card protects them from a raise. There are others who will not bet there if they don't have the flush themselves. You really need to start providing stats or at least some information on your opponents if you want meaningful answers.