I've had a couple of conversations with bike11235 and am including them here in case anyone has one of these tandems and is interested in potential upgrade paths.
Crankset
The original crankset on the tandem had pressed in rings so changing them wasn't an option. There was also no way to easily change crank arm length. We took the ratio of my inseam to crank length of 170 and applied it to my wife's inseam which gave her a crank arm length of around 150. She has short legs and was getting too much leg motion with the stock 170 cranks. We opted to pick up a custom set of cranks from DaVinci tandems which cost more than they bike. But they are light, they offer the ability to change rings and they came in the lengths that we desired. It was amazing how fast we rode after replacing the stock cranks.
BBs
I originally replaced the loose bearing and cone BBs with 68x122.5 sealed cartridge BBs which matched the length of the original crappy BBs. It was a night and day difference. When we upgraded to the new crankset, there were some spacing issues. I measured between the inner face of the new cranks and the outer face of the BBs and came up with about 8mm clearance on both sides. I picked up a pair of 68x110 BBs (un-26 I believe. Nothing fancy) and the fit was perfect. I have about 3 to 4 mm of clearance on each side now.
Front derailleur
The original front derailleur on this bike was horrid. I picked up a Shimano 105 triple derailleur and it installed and tuned very nicely. Anyone who works with them knows that triples can be a pain to get adjusted well. It took some effort, but this one works as expected.
Rear derailleur
The original rear derailleur wasn't anything to write home about but it was definitely in need of some attention. I ended up swapping it out with a long cage Ultegra off of a spare bike and it ****s great. The Ultegra has to go back on the donor bike so I picked up a non Dyna-Sys Deore which was the reason for this thread all along.
Wheels
The original wheels weren't anything spectacular but worked well enough until I found some replacements. I found a good deal on some 40 spoke rims on E-Bay for around $200.00. They are on the tandem in the image at the top of the thread. They have sealed bearings (4 in the rear) and are beefy rims. They are wider than I would like and probably would fit 700x32 tires very well. Out 700x28 Dura Skins fit well enough and they are very smooth. The good part about being beefy is that there is a lot of rim to dissipate heat when braking. With only one pair of brake calipers, tandems can generate some heat if braking on a long downhill descent.
Brakes
Brakes are the Achilles heel of most discount tandems. Our came with decent calipers but the brake shoes sucked. Luckily our local bike shop (Piney Flats Bicycle and Fitness) has some great guys. We were up there on the tandem and they thought it looked great. We are biased because I love the bike and it has become what we wanted. Anyway, while looking for some new brake pads, they went in back and produced a very lightly used pair of Scott brake calipers for $25.00. They work like a charm. I actually have to dial the braking back on them. So with the rims and the new brakes, stopping is not an issue.
Idler wheel
Egad was that thing horrible! It was small and had a lot of slop. There wasn't much friction, just the noise of the chain as it passed over it. Luckily, I keep all kinds of old parts around and I had some larger idler sprockets, with ceramic sleeve, from an old mountain bike derailleur. The increase in diameter and the tighter bearing made a tremendous difference. Now, you can barely hear the idler unless you lean over and make an effort to hear it.
Chain and cassette
I replaced the cassette with a wider range (11-34) and the chain so that I could run a power link. This was not necessary, but gave us more options.
Tandem $500.00
Crankset $520.00
Wheels $200.00
Derailleurs $100.00
Misc $200.00
Tires $ 80.00
So for about $1600.00 over the course of 3 to 4 months, I have a great tandem. Me and the wife are already over 800 miles on it so far this year. That doesn't sound like much, but she's never ridden before. We also have a lot of other irons in the fire so we can't do 200 mile/week averages like I was doing a few years back.
If you have any questions about these bikes, feel free to drop me a PM.