Which 2C’s do you have? I do believe the Sig series will allow 4 Ohm (8 is nominal). But, I would not want to dip below 4, as 4 is the minimum. Even the non Sig series from the 90’s I believe could go down to 5 ohm.
You could always stop by the Vandersteen web site User Forum and ask, and Richard could probably clarify.