And here is a start of story! Since after first power up I've recived E06 error tnan I've used a TFTP Boot recovery and Firmware flash.
Recommended by support service TFTP boot recovery 1.24 for all 4 models and firmware flash v. 1.40 or 1.41 are unsuccessful - both finished with E06 state. I.e. after flash I have E06 - long press device button - state LED signalling "firmware upgrade" by amber light - reboot - E06 again!
If you are starting from a clean harddisk, you'll to through E06 twice: first to partition the disks, then again to install the firmware. The second cycle is necessary since the first does not install files on the harddisk.
I did this successfully several times on a LS-WVL with firmware 1.40 and 1.41. According to http://opensource.buffalo.jp/ls-x-140.html
your WSXL shared the same firmware, thus should behave the same.