In addition to JL Audio's tutorial at http://mobile.jlaudio.com/support_pages.php?page_id=143 , I also found a message forum discussing a similar method to tuning the gains on an amplifier.
My Phoenix Gold Xenon 100.4 amplifier is rated at 100 watts a channel (4) -- I don't have the birth certificate, but I wouldn't be surprised if actual output was close to 120 wrms per channel at 4 ohms.
Since I'm driving the MMC6500s straight wired (no biamping), the 2 front channels are seeing a 4 ohm load right? As a result, I'm aiming for to set the amp's gain to see 20.0 V -- square root of 4 * 100 (4 ohms x channel output).
Using a 1 KHz sine wave test tone at 0 db, I had my stock unit's volume set to 30 out of 40 and adjusted the gain for the front channels that drive the MMC6500s to read close to 20.0V. I'm actually around 19.7x V. My end result was the gain ended up around the 2 o'clock position.
Now does that sound like it's too much??? Does it make sense?
Or is the fact that I'm using a line output converter (PAC OEM-2: http://www.pac-audio.com/products/oem1.htm) causing some sort of complications? For what it's worth, the gains on the LOC are set at halfway, which is the default.
Oh, I'm using a $90 multimeter that is true RMS digital multimeter.