See the DIMM survey and results for more information. It says so in the manual, but I've not tried it myself - DIMM2 cannot be used in this mode. Due to the age of the board it is highly unlikely that any further updates will be provided. As the 6x multiplier is a remapped 2x and 2.5 is a standard voltage option, no modifications were even required to the motherboard. This could be the sign of a dying motherboard, but try cleaning the contacts and the battery surfaces very carefully using an alcohol based cleaner and gently bend the contact to make a really good connection.
All Hard disks seem to be identified correctly.
If anyone has any ideas, or further confirmation of the types of devices I would welcome them. This is because the Multiplier is set to '2' which internally maps to 6x in the processor and the default voltage for this chip is 2.4V - so running at 2.5 is reasonable. I'll post benchmark results soon.