@flatback The input impedance is 10MegOhm. The unit has three knobs - Volume, Bass, and Treble - and a switch for the fixed HPF, which is fixed at 100hz. As I understand it, the volume is not saturation, but just pure volume. The EQ knobs are boost only, and fixed at 150 and 3.5K Hz, respectively. When used, the curves produce a dip at around 700hz, which is pleasing.
It's really a subtle thing, and depending on the set of the EQ, almost invisible. I say almost because there is an intangible heft and evenness to the signal coming out. I could blather on about upper harmonics being highlighted and other technical yadda yadda, but you kind of have to hear it. I suppose you could put it after the Felix, but then there's gain staging and two different preamp and EQ colors. Might be nice, but I couldn't say.
What is nice was the simplicity of the thing. Use the volume to light the limiter just a flash when you bring out Thor's hammer, EQ to taste with only 2 knobs, and keep the HPF on. That's pretty much it....then just focus on the music.