If you don't want to use TMPGenc internal encoder, you can change this to LAME by doing the following:
1) first download the LAME encoder (LAME originally stood for Lame Ain't an MPEG Endoder - well, now it is
) The latest stable version is lame-3.93.1. Unzip the contents of the zip file.
2) Open up TMPGenc. Now Go Option > Environmetal Setting from the menu. Click the audio engine tab. Click External Program radio button and browwse to the unzipped LAME execuatble. Click OK.