You would be able to simulate Eyefinity with SoftTH. However, I would not recommend this unless you already have 3 monitors. The 4000 series just doesn't support the hardware. Like i said, it can be simulated.
If you're going to be buying extra monitors, you may as well do it right and get the hardware that supports it.
As you can see, only a list of games are compatible with this.
Here is a list of games officially supported by Eyenfinity which is much bigger and has new games while the software simulation does not have new games:http://support.amd.com/us/eyefinity/Pages/eyefinity-software.aspx