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i was originally hoping to install a switch to flick between the two dashboards (like a friend of mine has)
If you wire up the chip following the instructions, then turning on with the power button will boot the chip BIOS (and therefore EvoX or whatever dashboard you install), whereas turning on with the eject button will boot the retail BIOS (and therefore the MS dashboard). No switch is needed for this.
Additionally, on the DuoX2 (not the LITE), there are two BIOS banks. There is a switch on the chip itself to choose between them. You *could* make this switch external (this is what spartan is referring to) but it's probably not what you want.
I think you should just wire the chip up according to the instructions. No need to have it 'always-on', you may as well have the option to disable it with the eject button.