I somehow succeeded to enable all of 256MB SDRAM at 133MHz, and to enable video using ADLO with original VGA BIOS, on EPIA 5000.
It now boots into GRUB in less than 2 seconds. :) (It's too fast for IDE drive to spin up, so I have to hit reset button after cold start.)
And, now a strange thing is happening. When I disable USE_GENERIC_ROM and enable BOOT_IDE to boot up the Linux kernel from LinuxBIOS directly, it hangs at "Allocating PCI resources...". It is before these options should take effect. What is happening??
With USE_GENERIC_ROM, memtest86 instead of ADLO as payload works fine (several passes ran without an error, so there is no memory problem).
Before I began tweaking DRAM and video registers, I was using BOOT_IDE to boot directly into Linux just fine.