I used to have the D-E915 and to my ears, it sounds nice. The line out quality is very similar to the E925 and EJ-01. However, just to be on the safe side, I would buy the D-EJ925 to get the best line out possible(newer discmans). I never auditioned the EJ-1000, but in my opinion, the EJ-01 and E-J925 has a very good line out.
I've been using a DJ-E915 for the past couple of weeks, and I am loving the sound of the line out. I've hooked it up to my MG Head OTL and the sound has been very nice, almost as sweet as my Sony DVP-NS500V. The NS500V beats it out with better hi-end and a more cohesive presentation, but for a portable source I think it's incredible.
BTW, I'm selling/trading an extra one. Check out my post under the On The Trade Block thread.