One of the first things I changed after getting the Helios was the rear wheel. I think the Alfine 8 is a dreadful thing - heavy with a not very helpful range of gears. SRAM Dual Drive is definitely the way forward (and upwards).
It's horses for courses and there are a good range of options with the Helios:
Straight derailleurs - light, cheap, not so tough, not too good a gear range, higher maintenance, inefficiencies from chainline
Alfine 8 - not so light, gear range for the flat, tough, minimal maintenance, medium cost, perfect chainline
Alfine 11 - not so light, useful gear range, tough, durable, minimal maintenance, high cost, perfect chainline
Dual Drive - lightish, extreme gear range, not so tough, higher maintenance, high cost, inefficiencies from chainline
Rohloff, - lightish, excellent gear range, tough, mega durable, perfect chainline, mega cost.
By tough I mean no parts to get bashed when manoeuvring the bike in and out of tight spaces like work bike sheds etc.
By low maintenance I mean mainly amount of cleaning of sprockets.
Inefficiency with chainline is magnified on a small wheel bike as the crank is closer to the back hub - and magnified further if the loads on the chain are doubled as with a tandem.
Personally I don't need any more gear range than an Alfine 11 and I like the tough, low maintenance approach - and can't afford a Rohloff, so that's what I will stick with.