I have a MP6,1 with three displays attached as follows... 1) TV connected to HDMI (Bus 0) 2) An Apple 27" Thunderbolt display connected to Port6 (Bus 0) 3) A 20" ACD with Apple's DVI-to-MiniDisplayPort connected to Port3 (Bus 1) I have a clone of my 10.9.2 MP6,1 system on a 1TB FW800 LaCie Rugged disk. I attach this FW800 to the FW800 port on the backside of the 27" Thunderbolt display and boot up from it. When I do this I'm finding that with a TV connected to HDMI (Bus 0), an Apple 27" Thunderbolt display connected to Port6 (Bus 0) and a 20" ACD with Apple's DVI-to-MiniDisplayPort connected to Port3 (Bus 1) I'm only getting the 27" Display to light up. As an alternative I created a clone of my 10.9.2 MP6,1 system on a 1TB LaCie Thunderbolt disk. I then connected this LaCie Rugged 1TB Thunderbolt disk directly to Port2 (Bus 2) on the MP6,1. Booting up from the LaCie I find all three displays will light up nicely. It appears to me that under 10.9.2 booting from any external disk attached to my primary 27" Thunderbolt display will not allow me to have multiple displays; 2 or 3 or more. Is this a documented limitation I wonder, or is it a bug. Somehow with this configuration for booting the system there's insufficient power going to the TV and the 20" displays even though they are both directly connected to the MP6,1 ports. I suspect if I were to connect the 1TB LaCie Thunderbolt boot disk to the backside of the 27" Thunderbolt display it still will not allow the TV and 20" to light up. I have not tried this mind you.