This might be due to some limiting applied in Renoise to prevent the sound from clipping. To achieve the same loudness level you’d have to pass the wav through a compressor or limiter instead of normalizing the volume. You can try to put a compressor on the rendered wav in Renoise, boost the volume and see if you can get the same sound as the original track.
To make sure there’s more to it then just volume change, play the rendered Wav in Renoise and check if there’s any change in spectrum and/or phase of the sound between the original track and the rendered version. You can find a good spectrum analyser and a phase analyser in VST format here.
Did the tracks you bounced contain some VSTi synth generated sounds or samples played using Renoise’s built-in sampler. I asked because I only experienced differences when rendering VSTi output.
–P/\ULiE PHONiCK