Hi Keith,
I've got a Corbin too and it maybe because of the one I chose (DT Stitch) but it's as comfortable as I could ever wish for. Everyone who's seen it or sat it has also commented on the comfort. I know that Pat sent his back for recovering and perhaps he will weigh in here....
I know that several Corbins I've seen are just as you say, hard as a rock and others are not (wojo's comes to mind here).
I hope you get yours sorted
