This follow up is a long time coming. The Amperex tubes were removed and replaced with the stock Electro Harmonix which firmed things up a bit. Also, my external sound card was outputting in +4 mode which turns out didn't mix well with the inputs on the Predator. After testing a few things, the output gain on the sound card channels was turned down to -10 (consumer level) with a further 20db reduction in signal level through the Echo Audio mixer interface. From there I just leave the volume knob on the Predator around 10 o'clock and it sings.
Schalk also confirmed the above would lead to better dynamics as he mentioned the inputs were designed with the input signal of a cd player/dac in mind.
The truth is this thing has a ton of power. Unfortunately in my small apartment I may never have the opportunity to see what it can really do if given enough room to play at louder levels.