Have you confirmed it's not the shape that's a problem for you? The Liberator is very wedge-shaped, and so are the SI saddles you pointed out. Personally I can't even begin to ride the Liberator - it's plenty wide for me in theory, but it's so wedge-shaped that it forces my sitbones well forward of the widest part of the saddle, and I end up with all my weight on my tender parts on the nose.
If you try a much more T-shaped SI Turbomatic let me know how it works for you ...
Speed comes from what you put behind you. - Judi Ketteler