I tried today to connect three displays to my mid2010 Mac Pro 8core on Radeon 5870 and 5770 with just one card at a time. Monitors are DELL 2412M and they have D-SUB, DVI and DP inputs. So:
I successfully coonected (with both cards) all three displays with this combination:
1. DVI - DVI
2. Mini DisplayPort - DisplayPort (with adapter cable MiniDP - DP, very cheap)
3. Mini DisplayPort - DVI (with MiniDP to DualLink DVI adapter)
All three displays were set to 1920x1200 resolution. One display simply shuts down in you try to connect it via MiniDP - DVI adapter instead of MiniDP to DL DVI.
So, you do not need two MiniDP to DL DVI adapters, at least not for 1920x1200 resolution.
Credits to this guy, he even connected two 30" dsiplays with this combo
http://tinyurl.com/9y4de3p
I successfully coonected (with both cards) all three displays with this combination:
1. DVI - DVI
2. Mini DisplayPort - DisplayPort (with adapter cable MiniDP - DP, very cheap)
3. Mini DisplayPort - DVI (with MiniDP to DualLink DVI adapter)
All three displays were set to 1920x1200 resolution. One display simply shuts down in you try to connect it via MiniDP - DVI adapter instead of MiniDP to DL DVI.
So, you do not need two MiniDP to DL DVI adapters, at least not for 1920x1200 resolution.
Credits to this guy, he even connected two 30" dsiplays with this combo
http://tinyurl.com/9y4de3p