[Overdriven]

Balancing is a must, for any charger or lipo battery. Personally I'd skip the 606I and go for the 720I its only $30 more than the 606I on RC-monster. You'll be able to charge the packs faster as the 606I is limited to a 50w output. On a 6s 5000 pack you'd charge it at 5 amps for 1C charging. With only 50W output availible on the 606I the max it can push is 2.25 amps making charge time twice as long while running the charger at its max.

As far as a power supply, 10amps would be the minimum. 15 amps would be better as you wouldn't be pushing the power supply as hard and could charge at over 1c if the batteries were capable of it. BrianG's speed calc page has a section about chargers + power supplies and matching them up to the batteries you intend to charge. Its worth a look.

Btw, my setup is a 615I (720I is a newer version of it) with a Competition Electronics 23amp powersupply. I love the charger and the built in balancing. Set it up, plug it in, and go, no worries. The powersuplly is overkill as I only charge 5s 6000mah at 1C, but I got a screaming deal on it and couldn't pass it up.