Do you mean at the soundcard input? I'm using my SSL 2+ Hi-Z input...and the signal inside Logic looks ok. When I use the preamp without the Reactor there's no problem. I don't think the problem is there but thanks for your inputIf you are putting a linelevel preamp signal into a instrument level device, maybe you need a reamp device????
What's the signal level at the preamp output? Do you have an oscilloscope? Or some other way to measure signal amplitude? What kind of preamp is it? If it's simply a 1:1 tube amplifier with only volume after EQ, and it's running at 300V, you'll easily have a few volts p/p. The Reactor only has a 9V power supply, so you'll need to severely limit the input signal to avoid heavy clipping and overloading.
Now I’m going to catch some heat for this and that’s alright.. but did you ever consider it’s not the power amp you are frustrated with and its the speaker and cab?