The switch and plastic lamp holding assembly on the energizer DB6AA and DB8AA lights can't handle even 2 amps for any significant time. The reflector can't handle more than about 9 watts for any period of time.
Before I got rid of all my DB lights, I typically rewired them so that the two barrels on each light no longer ran parallel, but were changed to serial. I found that the best reliable combination for the DB8AA was 7 NimH in serial plus a dummy cell overdriving a WA 1315 bulb rated at 6.27 V, 1.42 amps. 8.9 Watts, 178 lumen and 125 hours. The voltage drop through the high resistance switch assembly is significant. Unfortunately, I destroyed a few switch assemblies while rewiring.
Alternatively, if you don't use the AA battery sleds that slide into the barrels, you can fit 17 mm cells into the barrels. Each barrell of the DB8aa will hold your choice of 6@ cr123 cells, 3 @ 17670 cells, or 4 @ 17500 cells. I found that the barrells were tight enough that only certain unprotected Li-Ion cells like the Panasonics would squeeze in.
The easiest and least cumbersome DB setup was the DB4AA with 3 @ CR123 in each barrell running in stock parallel driving the WA 1315.
Finally, I gave up on the unreliable DB platform and moved on to various hot-wired mag mods. It was really a shame, because the serial / parallel arrangements to lower the 0.7 amp load of the stock bulb to 0.35 amps per alkaline cell was novel for the time.
As you said, the DB8AA stock bulb was rated at 5.5 volts and 0.7 amps. The DB6AA bulb is rated at 4.2 Volts and 0.7 amps. If you run your DB8AA's at 4.8 V on NimHs you can overdrive the DB6AA bulbs nicely -- much brighter than underdriving the 5.5 volt bulb.
Have fun.
