A little background here: I'm working at a mine this summer and when I came in I noticed 3 huge TV's mounted on an outside wall that were just sitting there not being used. I learned that the people who had ordered them planned to display images and scrolling data for the shifters to look at and make sure they are operating the correct equipment/compete for higher production but the people who ordered them failed to realize they didnt have a proper PC to run them.
You can get a motherboard with two PCIe X16 slots so you can have two video cards. That will give you 4 outputs. You can then hook up to the TV's by putting a DVI-to-HDMI adapter on the DVI outputs and running an HDMI cable to the TV's. Found a video card that is only $60 after mail in rebate.
Why get two of those cards when you can get one card that supports eyefinity and support up to 6 displays? AMD's website lists the following as cards that support eyefinity:
■AMD Radeon™ HD 6870 GPUs
■AMD Radeon™ HD 6850 GPUs
■ATI Radeon™ HD 5970 GPUs
■ATI Radeon™ HD 5800 Series GPUs
■ATI Radeon™ HD 5700 Series GPUs
■ATI Radeon™ HD 5670 GPUs
■ATI Radeon™ HD 5500 Series GPUs
■ATI Radeon™ HD 5450 GPUs
■ATI Mobility Radeon™ HD 5400 Series or higher GPUs
Should be able to find a single card to run your three monster Aquos' and not have to deal with two cards. By the way, I wouldn't mind having one of those just to put in the game room for my 360
As arson suggested, get an Eyefinity edition GPU. However, it should have at least one HDMI and 2 DP or mini DP so you can use adaptors (IDK if they make DVI to HDMI adaptors)
The graphics cards are really the most challenging issue. Since they can't be constantly maintained, I would suggest some of the cheaper, passive cooled ones. They will perform admirably with minimal issues.
EyeFinity is the way to go. From what I have read it seems that installing the appropriate video card that has the Catalyst Control Center will allow me to use one monitor (the one that will be hooked up indoors) to control what the other monitors (the 3 Aquos on the outside) see. It's just a matter of choosing the correct EyeFinity video card/motherboard/processor at this point.
ATI used to make DVI to HDMI adapters and that carried audio but I don't know if they come with cards anymore. However, monoprice.com makes every type of adapter you could imagine and a DP to HDMI adapter would be easy to get and since both protocols carry audio I'm assuming the adapters would too.
I would suggest a 5450, but be careful to buy the "eyefinity edition" or whatever, most of them are not. Alternatively, you can use a non eyefinity card and your integrated graphics, that is what I am doing now.