i notice that many burners' specs state that they can burn DVD-R DL as well as DVD+R DL. however, all i've ever seen for sale are the +R DLs, which do not play on the main DVD player in our house. commercially made movie DVDs that are dual layered DO play on the main home player. i'm assuming these are DVD-R DLs. i want to burn content on DVD-R DLs. where can i buy blank DVD-R DL discs? anywhere?