Well the problem with creating - or indeed playing - MP3/WMA content is navigating around the content using the LCD screen. The remote control has a design flaw here too in that it doesn't replicate the "Folder +/-" controls which are present on the top of the main unit. If you don't use "Folder +/-" then you have to scroll through every track in the folder (directory) before you get to the next folder. Given that anyone sane stores music in the \Artist\Album\Track directory format I think you can see where this is going? Although I have just noticed two buttons on the remote which don't appear to have a function - I'll see if they do Folder +/- but the rest of the post still holds true anyway.
In short you aren't going to be creating playlists on the DMX-25. I doubt in fact that you would manage to navigate the 293 artists and 1290 albums which we have on MP3/FLAC without losing the will to live
I think this unit is designed for portable MP3 players really (a Creative Zen certainly just appears as a mass storage device when plugged into the USB port of the DMX-25) where 999 tracks is not likely to be a problem.
I don't know yet whether the DMX-25 will accept externally generated playlists but even if it did then how often would you break the 999 limit?
NB - you can dump 999 tracks in multiple directories into a USB device and get the DMX-25 to randomise all tracks in all directories which personally is what I'd be more likely to do. Eg - pick music for a meal with friends which would perhaps be three or four albums randomised? I'm not sure whether that is practical design or laziness
Without fitting a much more expensive display and a touch pad/screen I'm not sure what the point of listing more than 999 tracks would be. If you think about your (small) MP3 players then you know perfectly well that you don't generally navigate that deep into the folder (directory) structure. You create some playlists on the PC and load them onto the MP3 player. I suppose an enhanced remote control with a display and softswitches would work but then again we're heading OTT for something that I'd expect to cost £80 next February.
I think the best thing for the DMX-25 would be to do the same. We have memory cards for a PSP and a USB adaptor (MobyMemory) - I think the best way for this might just be to write a few cards with MP3s and treat them as anywhere from 10 to 80 "CDs" at a time.
The memory is undoubtably the restricting factor to the number of tracks but having thought about it then it seems a reasonable design choice given the serious navigation issues.
I might sound negative but I'm very pleased with it. I do have umpteen USB devices which I can plug into it so my viewpoint there is probably skewed.
On the SD memory card side then this looks pretty simple given a 1GB SD card will cost you £8 or so and a 2GB about £12. I'll give it a try and see what happens but that would be quite attractive to me if it works as SD cards are smaller than USB devices