In Rhythmbox it's possible to disable compression for ReplayGain by unchecking a box in the settings of its ReplayGain plugin. The option is described like the following:
It provides configuration options for [...] enabling or disabling compression in order to prevent clipping.
I wonder if there is such an option in Banshee? I have checked in its menu and glanced under Banshee in the dconf-editor without finding anything.
The reason I'm asking is after reading the following in the ReplayGain specification:
The audiophile user will not want any compression or limiting on the signal. In this case the only option is to automatically and temporarily reduce the pre-amp gain below the user-selected setting for tracks where clipping would otherwise occur.
Banshee currently does neither; it doesn't handle clipping at all, merely applying the needed gain. This is somewhat less important given that it also doesn't expose the pre-amp knob so it's much less likely that the audio will clip in the first place.
So, the answer to the question “How do I disable compression for ReplayGain in Banshee” is: you do nothing; there is no compression for ReplayGain in Banshee ☺.
Banshee's ReplayGain support is largely influenced by what I care about and think makes sense from a UI perspective. There are a bunch of knobs that could potentially be exposed, but I don't think make a huge amount of sense, or should be automatic (selection of album versus track gain, for example).
Clipping prevention is something that probably should be implemented, though. At some point ☺.