Much more expertise in the above posts than I can hope to muster, but just by way of reference: our daVinci uses Campy Chorus Ergo shifters. The RD is a modified SRAM x9 unit which shifts any of the 9-spd cassettes I've tried flawlessly. The FDhandles a quad-ring 1/2-size chainring with what I believe is a custom FD. FD is not indexed, but after about 1000 miles and 1000 curses I got the hang of it. FWIW I much prefer the Campy shifters of the Shimano 105 brifters on my single, but the Shimano shifts flawlessly as well. I'll switch to 10-spd when my tandem LBS is convinced it works well enough; we're not a particularly strong team so I'm not going to worry about durability and our longer chainline gives us more cross-chaining latitude.