I don't know the Sirius, but there are two types of serial cable and you may have the wrong one. Wires 2&3 may or may not be crossed over on your cable and you may need the other type. You can either plug a "null modem" adapter into the DB9 end, or swap the wires over to find out.
Please note that if the Sirius is not using standard RS232 then you may have already damaged it by using the DB25-DB9 lead. All modifications are at your own risk.
Good luck :pint:
