Tetris Attack uses a newer format (the songs of Panel De Pon are somehow unsupported though) of the so called N-SPC engine, which is not fully supported yet, but with some messing around you can get it working. Basically try the "--np" command when converting to MML format.
It will display undefined commands such $fb $xx $yy, $fd $xx $yy, etc. $xx for $fb is usually the sample being loaded (in hex, just saying since the instrument list outputted by NintSPC is in decimal) but sue me for the 2nd value of that command, I have no clue. And as far as I know you will have to set the tempo manually, since this is not converted either. Replace all $fb $xx $yy with the sample loaded in $xx.
E.g. $fb $05 $01 would be replaced to PATCH005. $fb $10 $01 would be replaced to PATCH016, and so on. Remove all other undefined commands you see/find.
If I have the time I will update the tutorial for cases like this and explain it more detailed. Thanks for reminding me that way, lol.
Edit: Just tested it and it only display $fb with the song Yoshi's Stage (Critical). So you have to get the instrument with SPC700 player by looking which instrument is played. :<
Edit2: For proof that it works with quite a few tweaks I present you a badly ported version of Yoshi's Stage (Critical).