I use the same PSUs as Tony and I have the PowerLabs PL6 which is rated at 1000w 40 amps. Its a beast of a charger for upto 6s packs and will parallel charge like a charm. If thats to pricey then the new GT500 is the best option out there for charging 6s packs. You can get the DPS600-PB power supplies for dirt cheap and the GT500 will work on 12v but it will perform better on 24v. My PL6 handles up to 36v.
Personally get off the AC side and get on the DC side. I also have a 12v portable solution, a deep cycle boat battery. I am set for the field. Thats why you need to get off of AC, an AC only charger will need a 120v source to charge which means a generator if you go to the field. Last thing the POwerLabs product is being expanded to include bump charging. With a simple rf tag the charger will know what program to use and start charging without touching the charger, except to start charging. ALl the settings for that pack will auto load into the charger and setup everything for you once programmed.
GT500 with everything minus power supply (GT line)
GT500 with SPA
PL6 (cell pro line):
Cellpro PowerLab 6