Hoppin does address the issue of "diegoumenon". The linguistics are complicated (to me), but she suggests a couple of reasons why it might have been changed from an original feminine ending -- either to hide the author's identity, or to prevent the letter from being rejected if it was thought to have been written by a woman.
Another possibility is that the writer of Hebrews used a "literary plural form" in this verse, as is done in 2:5; 5:11; and 9:5 (lack of time, as in 11:32?).
Actually, I'm trying hard not to be offended at how much weight is being given to one seeming contradiction on a law professor's blog. If my own study (on this and other topics in this thread) is not to be considered at all, and if even the work of highly respected Christian theologians (including some from your own conservative Presbyterian tradition) is not respected, I'm probably wasting my time in carrying this discussion any further. It seems that you and Lydia have your minds made up already.

