I have Sigma speaker cables and are currently testing the omega. (Hopefully, will be able to post a review/comparison shortly). The sigma easily outperformed by Nordost Valhalla 2s. The omega is even better. But, this does not answer your question... so
Be aware that until you reach Alpha stage, the shunyata speaker cables do not have the HARP feature. This technology really does distinguish Shunyata cables and I believe is the major factor contributing the Shunyata's superior tonal and sonic character (in the cables with this technology).
I note that there is about a $2000 difference in delta vs alpha, but based on my (limited) experience, it is really worth the difference. I have seen alpha speaker cables used on this and other sites, so you may be able to reduce the difference significantly.