This is getting all too confusing.
Bottom line, 10 db SPL doubles the output. 70db is twice as loud as 60 db. 80 db is twice as loud as 70 db. 90 db is twice as loud as 80 db, etc, etc, etc.
Amplifier power, twice the amplifier power will give you 3 db more SPL. So a 200 wpc amp will give you 3 db more output than a 100 wpc amp. So you would approximately need a 1000 wpc amp to create sound twice as loud as a 100 wpc amp.
As for voltages, I'm not sure of the formula, but if indeed twice the voltage gives you 6 db more SPL, then Peak's formula sounds accurate. 6V would sound roughly twice as loud as the standard 2V output. The reason for this is normally so that a preamplifier is not necessary. Since the BAT preamps provide 17 db of gain, your Cary already provides 10 db of gain more than a 2V output, you could easily drive your Pass amps to their full output w/o a preamp.
All this really means is that you have much more gain than you need, and will probably be listening with the volume control turned down pretty low. Careful you don't crank it by accident, you could damage your speakers.
