Thanks for the picture. I am still evaluating recumbent rides that might help relieve back pain. A shorter wheelbase version of the Japanese Slingshot etadpole is what I am currently preparing to build. A dual recumbent such as your just seems like it would be okay for long straightway but not very good in stop and go traffic or even in the suburbs - maybe so with training wheels but then the cops might pull me over for having too many wheels. 
Maybe what you're looking for is a standard bike but with a little more relaxed body position, like the Dutch-style bike. The Dutch tend to build their bikes with steeper seat tube angles, which puts the crank (and the feet) farther forward of the hips. The head tube is also at a steeper angle than you usually see stateside, and has swept back handlebars which allows a more upright body position. The seats tend to be bigger & cushier as well. The whole package makes a much more comfortable ride, more akin to walking, which is far easier on the back than the typical mountain bike you find in the US.
With a few carefully chosen parts you can modify most any bike to simulate that riding position; a seat post that makes a bend backward, like on Mordaz's front-drive recumbent, a shorter handlebar stem, and swept back handlebars. I did that with my wife's bike a few years back; it was my daily rider for many years, but she didn't like the near-prone racing mountain bike position, so I did it up quite nicely. I actually like riding her bike better than my own. Very comfy! The one place the Dutch style doesn't shine is on hills (the Netherlands are flat as a pool table!); but the electric hub motor is the Great Hill Leveler, so you might as well be comfortable.
The photo below I nabbed from the
Gazelle website; they are the preeminent bike builder in the Netherlands.
