Q: need help to a upgrade to 4 monitors

Dear H.R.P. 1979

Wau !  4 monitors

Okay, you will need some help and some more Mac muscle, I think.

Try ATI 5770 maybe Sapphire 7950 (could work, beefier, but more expensive)

As far as I know, there are 2 outputs on each card, so you might need 2 grafic card

depends also how much picture you need for each monitor. If you want the maximum

then probably 2 cards. If not so much, then could be matrox double/tripleheader

i don't know where you live, so I don't know what's available there.  Nvidia has Quattro

4000 which is very expensive.

Grüße aus Kanada

John B

The ATI 5770 supports three monitors

All cards can support 2 x 30-inch, all DVI out ports, and MiniDisplay Ports with proper dual-link.

http://support.apple.com/kb/HT3382

http://www.atlona.com/Atlona-Dual-Link-DVI-to-Mini-DisplayPort-Converter-USB-Pow ered.html

Supported display configurations (Apple ATI 5x70)

https://support.apple.com/kb/HT4279

Note: If you are using an Apple Mini DisplayPort to DVI adapter, only two displays are supported across the three ports. If you are connecting three displays, any DVI displays must be connected to either the Dual-Link DVI port or must use an Apple Mini DisplayPort to Dual-Link Adapter.

you do not need $449 5870 you can have two 5770s or GT120 and 5770.

Mac Pro (Early 2009), Mac Pro (Mid 2010): Supported display configurations

Readers here have found that if you have two Brand-X Powered adapters, aka active adapters, it also works fine. These do not always require another USB. If designed recently, they can pick up a power pin in the Mini DisplayPort interface.

AMD (makers of the 5770 and 5870) lists the qualified POWERED adapters that meet their most stringent requirements. Look down the page and you will find several qualified Active Mini DisplyPort to various others, such as HDMI. These adapters are available from other outlets, such as Amazon, sometimes for far less than the Apple adapters.

http://support.amd.com/us/eyefinity/Pages/eyefinity-dongles.aspx

The other desktop monitor will plug directly into the DVI port on the card and the 40 inch tv will still connect via HDMI over the second Mini Display port.

That will work only if you use an active Mini DisplayPort to HDMI adapter.

The only (someone) have found to work (2009)

http://www.alibaba.com/product-gs/337561577/miniactive_display_port_tohdmi.html

thanks-just goes to show me that I don't know everything, that there are others here

who are more qualified to answer your question, and I can't always bat a thousand. I will swing and miss.

J.B.

Four displays with one card.

<http://www.evga.com/products/pdf/02G-P4-3682.pdf>

For those who casually want to know,  Malcolm supplied the spec sheet link for the four port EVGA GTX680 Mac Edition (US$600), features page here:

http://www.evga.com/Products/Product.aspx?pn=02G-P4-3682-KR