I'm new to the subject, so here it goes:
What is the best way to buy Japanese DRM-free music on line, excluding the iTunes Store (I'm using Linux)?

Should I take it as a "you're out of luck, pal"?

You might not totally be out of luck

One place I can think of is HearJapan. I just checked and they're DRM-free.

Thanks, that's a good start
However the selection is quite small (I wasn't able to find any of the artists I know!). I'll look around a little bit more.