If you are going to build a power supply, re-use the transformer, the bridge rectifier and the filter caps, forget about the schematic..you are not going to build another receiver.
The small caps are for suppressing RFI that the rectifier diodes can create.
The common ground connection you've found is Sony's way to prevent power line hum from ground loops. You needn't use the same technique if you want to build your own power supply to achieve a good common ground connection.
The taps are likely to switch between power line voltages, but again, you will be making your own circuit and you can choose to use either winding.
Your greatest concern with this transformer is the peak no-load output voltage which is higher than most low-voltage regulator chips can handle. There are switching regulator chips that can easily handle this higher voltage and deliver 3 to 5 A to create a step-down regulator and you can use a large heatsink from the old chassis to other make a zener-diode pass-transistor pre-regulator to develop well-filtered power at a voltage level that doesn't exceed the Max. V of the regulator and other chips of your power supply design.
If you still have the rest of the receiver, you can find you can obtain the zener diode pre-regulator pass transistor you need for free if the receiver used discrete high power transistors for the audio output stages.
Don't be afraid of creating a nice bench power supply of your own design that can double as a space-heater in the cold days of winter. If you chose in your design to go the way of a quiet pass-transistor pre-regulator, just recycle a small fan and other heatsinks and large toroids useful for your new original custom designed power supply. You might not even need a fan for cooling, but if you discover during development that things start to run a bit hot, a fan can be salvaged for free from an orphan or defective desktop PC power supply.
Don't worry, this global-room-warming effect will only be noticed when your custom-built power supply is outputting low-voltages at high currents with this transformer.