Hi

> Nobody try to record is A-100 with a sound card and use DI

Nobody answered, because nobody had the idea to do so. ;-)

A DI-Box is not necessary (but of course not wrong) for line outs of
usual synths as long as the connection between the synth and the input
of the mixing desk or the soundcard is short enough (not longer than 2
or 3 meters), and if the input is a line input too.

You only should use a DI-Box if the cable length is longer, and the
input is a balanced (Mic-)input.

Florian