However, as I look at your current setup and price for upgrades, I would suggest that you change the front granny ring to a 24, keep the other two rings and and keep the current cassette as is (11-32, if I understand correctly). Using 24/32 gives you 20.25 gear-inches whereas using 26/34 gives you 20.64 gear-inches.
Another suggestion for your setup would be to disassemble
your 11-32 cassette, buy a 11-34 or a 12-25 cassette, disassemble it also, and cobble up your own with closer ratios at the top and wider near the bottom. Hints on how to do that http://sheldonbrown.com/k7.html
BTW, my tandem has 48-38-24 front and 13-15-16-17-18-20-23-26-34. Not to tell you that you should go that way, but rather that it could be done.