The wife and I actually met up with our friends last night at a local bar. This girl I am hot for was there with them, and I actually spent some quality time sitting next to her and chatting. The couple she was with is a couple we've swung with before, and she has had at least one encounter with them (along with a fourth male).
I still haven't managed to pull the trigger with asking her out. I just need to somehow muster the courage. I guess it could happen through getting together with this couple at some point, similar to the foursome she's apparently experienced with them already. But I would also love a good FWB that I could date every now and then.