Orange amps have almost no headroom, without hearing the fizzy sound your talking about I can't say for sure but my guess is that's just the way it rolls? If the preamp is adding any gain at all that would be a reasonable result from an Orange head??? They are great plug & play amps if you want classic to heavy metal distortion but they don't make very good Jazz amps? Try to ristict the signal some with a E.Q., it might help some? I have to do that with my Orange if I want any kind of decent clean tone out of it & even with the amp restricted it starts breaking up around 10:00???
When you say "runs out through the preamp" do you mean a direct line out to a board or recording interface?
What you describe sounds like most preamps out directly to mixer or recording interface and get real fizzy because they don't hit power amp/speaker emulation. Have you tried a DI box like a redbox or similar cab sim?
Some amps have it and some don't. If you have any modeling software you can hear the same thing when turning off cab emulation. Fizzy mess and really thin sounding.
Preamp outs need a speaker sim to sound a lot less crappier. It's because guitar speakers typically filter out the crappy distorted high frequencies that you're hearing from the line out.
In twenty first century Roland Cube amplifiers, the effects of a power amp stage are part of the digital modelling. The actual power amplifier is a simple, linear, "make louder" stage.