MK2 Boxed Hiface with internal 5V supply & internal battery charger
The cost of this is €270 + shipping €20
What you need to provide is a 9V to 12V external power supply - this powers the regulators when the unit is switched on & powers the battery charger when the unit is switched off - see below
This is a plug & forget arrangement.
These Hiface modifications are performed on the important circuits. The existing 1.8V & 3.3V switched regulators are removed & replaced by ultra low noise regulators. The clocks powered from a 3.3V battery. This low noise 3.3V regulator powers the output stages of the Xilinx chip & the output stages of the SPDIF generating chip.
A word about the external Power Supply
Some consideration should be given to the external 9V to 12V power supply. Yes the switched mode power supplies that come with most modern appliances WILL PROBABLY DO - you know the light ones. But it is better to use a better quality PS i.e. probably one with a transformer in it (i.e heavier). Remember, this is the feed for the 5V & 3.3V regulators in the MK2 modified Hiface box so the cleanest possible power is advisable.
A suitable UK 9V DC supply is £14 here but others may well be available locally in your area.
A suitable US 9V DC supply is $10 here but again others may well be available locally in your area.
What you want is (v to 12V DC supply of 500mA or greater output with a 2.1mm plug with positive centre contact.