Have set up a 26"-wheeled Peri for a 6'4" guy with shorter stoker; stoker who is 5'3" also wanted to pilot same tandem with her kids.
Solution was to order the new tandem with an uncut steerer tube and use lotsa spacers to adjust stem height for both the tall and short pilots, utilizing an optional Co-Mo adjustable pilot stem so reach could be adjusted for short and tall pilots. Worked great for them.
At 6'6" you may be stretching the fit limit a bit.
A Delta stem extender could bring up the pilot's handlebars sufficiently enough to suit you.