Beans, I'm wondering if you can speak with Clearaudio and find out if there are any MC output resistors that could be changed to bump your output up past 64 dB. Or maybe there are some users out there who have done this.
Here's the thing: My Classe Six was "fixed" at 57 dB but the unit came with a slew of loose resistors the owner could use to change the output in 2 dB increments. When I bought the XA, I changed out 2 resistors (one each channel) to bump the gain to 65 dB. There were other resistor choices that would reach as high as 75 dB!
No idea if this would be possible with your Clearaudio, but asking around and researching are cheap. BTW, so are resistors.