The ride profile of a recumbent trike is very different from a DF. Given equal 'engines' the trike will be slower up hill by quite a margin, slower on the flat by a (very?) small margin and seriously faster than the DF down any kind of hill worth the name.
When out with a mixed group it behoves the DF riders to let the trikes pass on the down hills, and the trikes to return the compliment up hill. While the trike will almost certainly be slower over the whole ride the difference is not that great, if this method of riding is used.
In my experience Big Apples at 70psi can be pretty quick, although if you are fast enough on the flat to make aero a consideration they will get draggy at 15-20mph+. I've used Kojaks, which were no faster than three Big Apples, Marathons, which were much slower than Big Apples and Marathon Racers which are a bit faster than Big Apples. I'm told that Marathon Supremes are pretty good and Trykers are excellent.
I'd ditch the Marathon today if I were you! I sympathise with your husband, but when my wife rode with me, on an identical folding bike, I felt I'd not done any exercise while she had been working hard. I was cycling nearly every day including a 16mile there and 16mile back commute to work. She rode once a week. If your husband were to descend all hills at close to walking pace then works to catch you up on the flat and up hill he'll get a better workout, but frankly if your fitness levels differ by a fair amount a tandem of some sort is the only answer.
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