There are 3 differnt kinds of DVI "adapters"
DVI-I which outputs on both digital and analogue, and that you have on most graphics cards, and thats why you can plug a dvi to vga or dve to HDMI and it'll work (not both to go from hdmi to vga though)
DVI-D which is ONLY digital
DVI-A Which is ONLY analogue.
And I think theres a new on coming out that supports sound, Much like HDMI 2.1 *shrugs* but am not to sure wtf is going on there.