Basically the Radial Pro-Rmp has an attenuator which many choose to mod and bypass because of the low output level. I have also experienced this low level output with my interface (Focusrite 8i6) and Pro-Rmp. I know also that some other re-amp boxes do not have such attenuation at the input, however technically the attenuation should remain there to convert from line level to instrument level, no? At the same time (if I remember correctly), playing a guitar track through the re-amp and amplifier results in a lower volume than plugging straight into the amp.