Can't help you much with the DirectTV grabber, I use zap2xml and it seems to work fine http://zap2xml.awardspace.info/ though it does need you to create a free account on zap2it.
Ensure that you've named your XMLTV channels in TVHeadEnd exactly the same as those in the XMLTV file, then go into the xmltv page in tvheadend and save your preferences (which should cause the xmltv grabber to be run), it should then tell you how many new events were injected into the EPG.
