The original question asked on this thread was along the lines of "How do I improve the brake performance on my e-tandem that is fitted with Shimano single piston disk brakes. The answers given by several people were along the lines of "get yourself some big honkin 4 piston Downhill brakes", which seems to have solved the original question nicely.

And finally, someone had to come along and wax nostalgic for the "good old days" and Arai drum drag brakes. In their day they may have been the best thing available. A lot of things have been the best until something better came along. For a touring tandem, disk brakes are better. They are lighter, they are cheaper, they have more absolute stopping power, and they are more reliable. They just need to be of an appropriate size for the mass they are asked to stop. Does anyone here still drive a cable actuated drum brake automobile?

Hope started making disk brakes for bicycles in 1989.and by 1995 they had gone over to hydraulic actuation. Not exactly brand new technology.

The only possible issue with a disk brake on a touring tandem is heat buildup. Are you going to tell me that an Ari drum wouldn't overheat? The solutions are to increase mass, improve cooling, improve brake performance at elevated temperatures, or some combination of the above. Shimano's aluminum core rotors are fairly good and I have one on the front of our tandem.

The rear brake is for speed control on long hills or for gentle stops. It is only in the role of speed control that any issue arises with disk brakes. The thermal load is enough to drive some brake sets beyond their working limit. There are solutions to that issue: improve cooling, increase mass, or improve thermal performance. The Hope solution worked well for me. The larger mass V4 caliper with multiple ceramic pistons and a vented rotor have shown themselves to be adequate for a 500 pound load. Additionally, the rear brake alone is capable of stopping the tandem, all be it at a lower rate than when it is used with the front brake. This is not marketing biz. It is my experience and the wisdom of the market agrees with me.

An Arai drum is a completely unworkable solution for the OP, and I doubt that even if it was possible it would solve the issue of single stop performance.