Part of the problem is that its a difficult speaker to upgrade from. They're so unique its hard to look at those speakers from an upgrade/downgrade perspective. I can't think of another company that makes a rough equivalent to the 1SC. Maybe Living Voice vs full size ProAc's, but I don't think they make small speakers. Maybe you can list some specific qualities that you need to improve upon over your 1SC's, and start there.
Also, maybe you should consider keeping the ProAc's and upgrading something else in the system. The 1SC's being driven by my VAC 30/30 sounds exceptional. Moving to an amp like that, and possibly a matching preamp can do a lot for the system. Dynamic contrast, image size and scale, depth, are all things that can get better without even changing the speakers.
Also, maybe you should consider keeping the ProAc's and upgrading something else in the system. The 1SC's being driven by my VAC 30/30 sounds exceptional. Moving to an amp like that, and possibly a matching preamp can do a lot for the system. Dynamic contrast, image size and scale, depth, are all things that can get better without even changing the speakers.