Move the couches to a different location, and see if the smell follows.
A possible explanation that leaps to mind is that the access opening they used was closed during daylight hours, trapping one or more skunks in the crawlspace. With no escape, these animals could have died and begun contributing a slightly different odour to the cocktail of smells you already enjoy.
I would be very cautious about going in there if you think there are still live skunks present. If they feel that they are cornered, their reaction will be predictable.
The couches are big. They literally wouldn't fit anywhere else. I will be cautious.