If I may be allowed to jump in here as a complete newcomer to the forum?

IME (and many others) not all mp3 encoders are created equal and some are even faulty.

One widely consider excellent, if not the best, is an encoder called LAME. It seems to be in a state of continuous development, much like Audacity, and gets better and better.

Unfortunately LAME is a command line driven program but can be front ended with RazorLAME which passes the necessary parameters to LAME and can batch files to be converted.

My experience of using these converters leads me to believe that sometimes a wav recorded to near 0dB can create an mp3 that goes into clipping, but not always. I make sure that wavs for conversion are a few dB down. 2 or 3 seems good.

I use a Denon DN-C615 for playback of wavs and mp3s. The mp3s seem indistinguishable, to my ear (an old one), when recorded at the LAME "extreme" setting (320kbps).

LAME can be found here: http://www.rarewares.org/mp3-lame-bundle.php
and RazorLAME here: http://www.dors.de/razorlame/index.php

But it's only my opinion.
C-clef.