HT2848: Mac Pro (all models): Graphics card compatibility between modelsLearn about Mac Pro (all models): Graphics card compatibility between models
Currently Being ModeratedJul 24, 2013 12:49 AM (in response to ticketmack)
HD5770 is supported by Mac Pro 3,1 with OS X Mountain Lion.
Currently Being ModeratedJul 24, 2013 4:53 AM (in response to ticketmack)
Apple's right? but yes audio is not supported even though the CARD is.
Apple Mini DisplayPort adapters: Frequently asked questions (FAQ)
Guide to Apple graphic display adapters needed
You can connect a DVI to HDMI adapter or cable to an active Mini DisplayPort to DVI adapter but that won't give you any audio over HDMI. You could connect the DVI displays to the Mini DisplayPorts with active adapters and use a DVI to HDMI cable or adapter from the DVI port to the TV.
If you want audio via HDMI, you can use audio from the Mac Pro's optical output with this DVI to HDMI converter: