• upgrade BIOS to CDV_T24 X64 (I had 100% CPU (kworker) usage with T22)

• prepare USB drive (replace X with your drive number)

dd if=debian-7.0.0-amd64-DVD-1.iso of=/dev/sdX

• connect USB keyboard and VGA monitor (HDMI is not an option at this stage)
• disable UEFI Boot in BIOS (or use live image, it didn't work for me with official images)

BIOS → Main → Boot Features → UEFI Boot

• change BIOS settings to boot from USB

BIOS → Boot → move "USB CD" above "ATA HDD0: AFAYA MDS 1GB"

• boot from USB drive and install Debian

... on Wheezy:

• apt-get install grub-efi-amd64

adding ThecusOS to grub

• add to /etc/grub.d/40_custom

menuentry 'Thecus Normal' --class gnu-linux --class gnu --class os {
        insmod gzio
        set root='(hd0,1)'
        linux /boot/bzImage ro root=/dev/ram0 max_loop=210 console=ttyS1,115200n8 mem=4G
        initrd /boot/ramdisk
}
menuentry 'Thecus Backup' --class gnu-linux --class gnu --class os {
        insmod gzio
        set root='(hd1,1)'
        linux  /boot/bzImage ro root=/dev/ram0 max_loop=210 console=ttyS1,115200n8 domb
        initrd /boot/ramdisk
}

• update grub (update-grub command)

controlling fan

• install kernel >= 3.3 (3.2 doesn't have recent enough it87 module for ITE8728)

• set it87's fix_pwm_polarity option to 1 (without this pwmconfig will not find fan)

echo "it87 fix_pwm_polarity=1" >> /etc/modules
rmmod it87
modprobe it87 fix_pwm_polarity=1

• install fancontrol

apt-get install fancontrol lm-sensors hddtemp
pwmconfig # follow instructions
invoke-rc.d fancontrol start