Ok...so I got it running, but I realized the key is not static...it seems to change after a while (I don't know how long but at least every day if not sooner you will have a newer key). So I had to modify the script to be able to obtain the key first, and then pass it as a variable to the script ...

so for those wonder "How the heck do I get this into a xml file on my NAS/Linux server?!"

curl --compressed http://api.hdhomerun.com/api/xmltv?DeviceAuth=Your25digitkeyinstead > tvlist.xml

Replace Your25digitkeyinstead with your key of course, and tvlist.xml can be whatever file you want to name ...