Hi Obdo,
You didn't mention if you have any of the following items hooked up and working. All are necessary to run Legacy engines from the DCS app.
MTH #50-1032 DCS/Legacy cable
Legacy CB-2 command base - usually part of the #990 Legacy set
#6-81326 Ser 2 serial converter
#6-81499 DB9 power cable
Do you have all these items? If so, have you tried running from the Legacy remote or DCS remote to test if all the conections are working?