Mod note: I've deleted the debugfile from the public post because it contains potentially sensitive information about your NAS. Any mods who want to look at it, it's archived in Old Threads.
The debug files are simply a large tarball. If you extract them on a UNIX host, you can investigate stuff like dump.txt to see information about the configuration of the system, anything that was in the system message buffer, etc. I did look at your system message buffer (dmesg/dmesg.boot) and there was nothing I noticed there. Unfortunately there's a huge amount of information to comb through and I don't look at these often enough to automatically know where all the juicy bits hide, and since it's a holiday, I don't have much time to spend on this.
If your system contains an IPMI/BMC/DRAC/other out-of-band management, don't forget to see if any platform level events like a power failure were logged.