Since the release of snom ONE plus there has been an update to the kernel, that is why there is two options. However you seem to not have upgraded sangoma after the update. centos 2.3 is correct it is using the kernel 2.3 not the old kernel.
sangoma's drivers are compiled to the kernel, so after the first run of updates (to the web interface and kernel) there is a reboot to load into the new kernel. sangoma will then be allowed to update, it would appear that your drivers are missing. Can you submit this as a ticket and have support check this box over, they will require you to portforward 22, 7783, 9090