mp3 is a form of lossy compressed audio, so that right there pretty much explains why you can't convert a wave to "uncompressed" mp3 file. if you don't care about file size, why convert them at all? Just leave them as wave files....
On another note, encoding an mp3 at 320 kbps does not mean you are getting the best quality. The encoder is much more important. LAME is by far the best mp3 codec, and also you get MUCH better results using VBR (variable bitrate) method than CBR, which is constant bitrate like 128, 192, 320... When converting a wave file to mp3 using LAME and VBR settings, you no doubt create the best quality mp3 file possible, but as the format is lossy, it is still not as good of quality as the original wave.
On option you might consider is FLAC, which is a lossless format of compressed audio. Their file sizes are larger than mp3s are, but if size is not an issue then perhaps FLAC might be a good option for you. Most all players such as winamp support flac and other lossless formats.
If you decide to convert your wave files to a compressed format, use dBPowerAMP. It is free and the best convert tool I have come across. You can find the link to its website in my sig below...be sure to download and install the proper codec from its website as well.
