That is a pretty vague question. To what end? What are you trying to do? One of those cards is a legacy card and no longer supported under new drivers, so why would you want to?
Sounds pretty specific to me.
This is not for me it is for someone else on another forum (tomshardware) who has 2 cards and is using the RX-580 and 2 of its HDMI ports for 2 of his monitors and has a 3rd VGA monitor and wanted to know if he could use the HD6450 in his PC at the same time.
I found out the answer and told him to use an active DVI to VGA converter cable from his RX-580 and that the HD6450 would not work at the same time because of the drivers.
I am a 30-year tech support person myself but I had never come across this particular issue.
Glad your found your answer.
Specific would have been I want to use the card to drive another monitor.
That RX 580 is very capable of driving all 3 monitors by itself and adding a second card would be pointless IMHO just to add a third monitor especially being a legacy card with no current drivers. I would recommend to that someone else to get the correct Display port or HDMI to VGA adaptor depending on the other 2 connections being used.
Apparently he is using the 2 HDMI ports and wants to use his other GPU for his VGA monitor.
I recommended that he buy an active adapter converter.
Thanks for the input.