I picked up a HD-A1 at the local BB (Charlottesville, VA) but unfortunately there were no titles to be found.
Anyway, I set it up on my "bench" as follows:
Turned on DHCP and it immediately came up on my LAN:
Close up of the main PCB, looks identical to the XA1, in fact the board is called PC-DIGITAL-XA1:
I also popped the front cover and it looks like they are using an internal PC HD-DVD drive. It appears to have a regular power connector and IDE interface on the back.