With the separate connector types I am seeing the following in IOJones after searching for gfx and looking at the corresponding AppleIntelFrameBuffer@n value.
HDMI and DVI both have the same connector type: 00 08 00 00 while DP has 00 04 00 00. This value shows up whether that type of cable is connected or not, so it may be pre-defined to always appear.
The av-signal-type for the HDMI connector matches its connection type 00 08 00 00 but for the DVI, it changes to 00 02 00 00 and for the DP cable it is 00 00 00 00. This av-signal-type value only appears for the actually connected cable.
The audio-selector has the same value 64 70 34 38 for both HDMI and DP but does not appear for the DVI connection.
The audio codec info does appear for the DVI connection with a value of 00 01 05 00 while the HDMI audio codec value is 00 01 06 00 and the DP value is 00 00 00 00. This value also only appears when that cable is connected.
I am not sure where to look to find the connector type of the connected device or if it is specified (for cases such as when someone uses a dvi-vga convertor or hdmi-whatever convertor).