Chris,
If I understand your charger correctly, you can charge 4 packs at once on individual outputs. Of course you can balance each pack individually, not like parallel. If your 320 watt charger puts out, not intakes 320, then you can charge 4x4s packs at 80 watts each. Round numbers 15 volts at about 5 amps each pack or more than 1C, total 15v x 5 amp x 4 or 300 watts. That is a slow field charge when you are waiting from full flight discharge, but not so bad in the morning at home if you start from storage charge of about 50%. If you need about 1500 mah input for each, perhaps with the end slow charging, say 30 minutes for all 4.
With parallel, you don't see the individual packs. For a 3000 mah pack x 4, the charger sees a 4 cell 12 amp pack. It still sees cell 1-4 on the balance port, but those cells are each 4 actual cells. You may need to use a cell checker to look at individual cells or occasionally check the individual packs/cells with the charger. Better chargers also look at internal resistance, another good measure of how the cell is doing.
Hope that helps and does not confuse the issue.
Fred