I got a similar effect by constructing a purpose-made monitor shelf. It's not as good for having a wide area open for large items, but it allows multiple levels for stacking, which works out great. It has one low shelf inside, just high enough to fit a keyboard and hands underneath, and then the top surface to put the actual monitors on. Keeping the bottom floor clear makes it easy to slide the keyboard in to make some temporary room in front of the structure, and the inside shelf provides a large general-purpose cavity for papers, mail, snacks, or what-have-you. There's also some room on the top to pile things up next to the monitors.

The original goal was just to get the monitors up to eye level, but I ended up enjoying the extra space at least as much.