I was unaware that there was a projector limit. I bought two video cards to eventually support three and four projectors. Can you post a reference? I haven't seen this in my earlier research.
If this is true, do you know why there is a limit?
NVIDIA Surround mode has always only been triple-display. AMD Eyefinity however is 2, 3, 4, 5 or 6 displays. The devil is in the details when it comes to surround screen gaming.
Do you want the political or the technical answer?
The political answer: NVIDIA never intended to take triple-display gaming seriously until AMD produced Eyefinity. NVIDIA develops under a closed door system that finds product input from customers to be a legal liability. They don't want to be seen developing something that a customer has given them the idea for. It's a very different culture than AMD has. AMD saw what Matrox did with the TH2G boxes and made it plausible on the driver level. AMD seeks customer input to evolve Eyefinity and exand it to the needs of the userbase. That meant accomodating a rather wide range of dispaly options. That ended up being 2x1, 3x1, 4x1, 5x1 and 3x2. NVIDIA never saw the merit in the multi-display gaming niche market. The only reason why NVIDIA Surround exists in any form to day is to bare bones feature match the most common AMD Eyefinity configuration, 3x1. They made their feature set to target AMD, not the consumer.
The technical answer: NVIDIA's archetecture is setup where a single card can only push out two ports. Back in the time of WIndows XP there was something called Horizontal Span Mode that enabled the two ports on the card to span in games. This feature was dropped from further development with the release of Vista and DirectX 10. For years NVIDIA dominated the triple-head gaming market thanks to the power and capability of the Geforce GPUs and the Matrox TH2G boxes. NVIDIA's tunnel vision never saw the market opportunity they had to maintain and grow that market with their hardware. The meant that for almost a decade now we've had that two port maximum from standard NVIDIA consumer line. When AMD Eyefinity was released NVIDIA was caught with their pants down and lost their market share for triple-head gaming hardware. NVIDIA still didn't see or understand the market, but they needed to come up with something to combat it within their current video card archetecture. For awhile they had been tinkering with S3D capability with the 3D Vision kit. This niche market also was about the same fit as triple-head gaming is as far as market size and future growth. NVIDIA handed over to the 3D Vision portion of NVIDIA to develop a solution to combat Eyefinity. The only way they could do it is to leverage the port configuration given by SLI. This meant that they had to figure out how to make port spanning work through the SLI engine at a driver level. NVIDIA needed something out to combat Eyefinity and quick to market means features were going to suffer. What suffered with NVIDIA Surround 1.0 was no variation in display count.
AMD is phasing in Eyefinity 2.0 after two generations of success with Eyefinity. I'm most interested to see what NVIDIA Surround 2.0 might plausibly bring to the table. Noone knows though because NVIDIA develops features behind closed doors with no input from customers on future designs. We have no idea if Surround 2.0 is in the works or if it will show up anytime soon to properly address the lack of port options on the NVIDIA side of the fence.