I have just found out how to convert midis to SSEQ for pokemon DS games.
you will need:
Kiwi DS Editor
(May need to google these)
1.rip the song you want to change. use Editor to find the sdat file, and rip it. Open it in VGMTrans and find the song you want to replace, and right click, and convert it to midi.
2.use the midi you just ripped to figure out instruments for your new midi. after changeing the new midi's instruments in FL Studio, export it to midi.
3.Open the newly exported midi in your hex editor. look for the byte x0c (the 12th byte) it should read "0060" change it to "00C0" and save. then reload the midi in FL Studio
4. The midi should be 2 times as fast, this is what we want. export it to midi, and overwrite the old one if you want. we wont need it anymore.
5. open the midi in hex editor yet again, and this time, change the "60" to "30" and save. Now test the midi in windows media player, and it should sound normal.
6. drag the midi onto midi2sseq.exe, and the sseq file will be created (maybe in the users folder ex. C:\Documents_and_settings\Owner\)
7. open your new sseq in a hex editor, and search for "FFC0" for every time you find an "FFC0" change the "C0" to "C7" and the byte after it to "00" there should only be about as many "FFC0"'s as there are channels in the midi. Save
8. load the sdat in editor, and find the sseq you want to replace and take note of the adress in the sdat. open the sdat in a hex editor and go to that adress, and open the sseq you just edited in another window. copy all the data, and paste it into the sseq. Save
9. test in VGMTrans, and it should sound good if done correctly.
10. use NDSTS to replace the sdat in the rom with the edited one, and test in game. DONE
Hope this helps, because it had me stumped for a long time, but the key was the "C7" calls were missing at the beginning of each track