QUOTE(NIXin @ Dec 5 2007, 12:11)

...
I didn't hear any difference on 5 samples. The 6th, which was a 10 second fragment of Imaginary Day by Pat Metheny, was my savior

Finally, heard some difference ...
Congratulations: you do hear differences between Lame 3.97 CBR 320 and the original, and you did so with your 6th track you tried. That's very good.
So you are a valuable member here as you do have fine hearing.
As for your initial question:
You are able to hear differences when giving all your best within a situation that has nothing to do with practical listening even when listening carefully, but it looks like the differences were subtle and they are audible only on rare occasion.
That's the world of mp3 (and other formats), and it looks like it's not a real problem to you when used with your palm.
You may want to consider variants:
The current 3.98 development (it's in beta state) is very promising with respect to improving quality even further. Use 3.98b5 if you want to give it a try (with the currently published 3.98b6 it's not totally clear whether the Lame devs wanted to have it published at the current state - it's not the Lame devs who do the publishing).
You can save some disc space by allowing for a lower bitrate than 320 kbps. IMO using --abr 270 yields the same quality in a practical sense as -b 320 while saving ~15% of disc space. It's not necessarily 270, and you can try a lower value. Most people here prefer a VBR method, and with 3.98's VBR has no issue any more according to my experience. So you may want to try for instance -V1 to get at a bitrate of ~225 kbps on average. As quality is paramount to you I wouldn't try other settings however yielding even a smaller filesize though usually quality will be fine as well.
In case you don't like mp3 etc. despite (or because?) of your test you may want to give lossyWAV a chance.
lossyWAV makes those least signifant bits of the wave samples to zero in a way that is done safely - safely according to the principles of lossyWAV. Using an appropriate lossless codec like FLAC on the lossyWAV result provides for an average bitrate of ~350 kbps when using LossyWAV quality level -3. All our listening experience so far shows up transparency even for this lowest quality setting.
So if your DAP is able to play FLAC or another appropriate lossless codec, you can go this way.
Look at the lossyWAV thread in case you're interested.