which makes the biggest difference? the worst one in the worst application that you upgrade.
i've had it be the amp PC, the IC off the source, the PC off the source, the speaker cable.
but never the digital cable! so there!
(in all seriousness, there are no hard & fast rules; i thought if a component had a well designed power supply it would be immune; the Esoteric XO1-D2, which is built like no other player, disproved my theory with its sensitivity to power cords).
i've had it be the amp PC, the IC off the source, the PC off the source, the speaker cable.
but never the digital cable! so there!
(in all seriousness, there are no hard & fast rules; i thought if a component had a well designed power supply it would be immune; the Esoteric XO1-D2, which is built like no other player, disproved my theory with its sensitivity to power cords).