I build my own 0844 firmware fos DS-106. For german-reading user have a look at http://www.synology-forum.de/showthread.html?t=6367
First I compared 731 firmware for 106 and 106j and found following differences
in hda1.tgz (filesystem for systempartition)
zImage(kernel) are the same. So I took 0844 for 106j, changed settings in .conf files and gave zImage and rd.bin a new ppcboot-header. I put pci-hutplug stuff for eSATA from DS-107 to hda1.tgz and adjust VERSION and checksum.syno. So I have a 0844 .pat file for DS-106.This is experimenal, use it on your own risk! You may lost all your data, maybe your DS isn't working anymore, if you are in warranty, you lost warranty. There is no support from Synology.
This file is only for DS-106 and DS-106x(128MB RAM), NOT for DS-106e