You must have extremely large midi files.

I copied Technote midis (which are probably smaller than average) to the supplied 8 MB card. I got 94 midi files on the card with only 45 % of the space used according to the 7k display. This was about 3 MB worth.

I then copied Tune 1000 midis (which are probably bigger than average) to the rest of the supplied 8 MB card. This was about another 3 MB worth. I ended up with 171 midi files on the 8 MB card.