I have the S/300 series I. It weighs 25,5 kilo according to the manual. The inside looks like this:
Underneath the shielding there are two 700 W toroidal transformers. It utilizes 14 transistors per channel and two 60,000 uF powercaps. The 'optical bias' version is a mk. II , although there are mk. II's without optical bias. I'm guessing they will have the same specs.