The Magnavox ZC320MW8 cannot play or record DVD-RAM discs.
See page one of the ZC320MW8 Quick Guide or page seven of the ZC320MW8 Owner's Manual for that and other disc compatibility information.
Most current TDK discs are manufactured by CMC, the same as the dreaded Memorex and several other retail brands. CMC media is regarded as landfill material.
If one must purchase blank media at a retail store Verbatim is the brand to buy.
Avoid 16x media for use in stand-alone DVD recorders. For stand-alone DVD recorders 8x media provides a better burn with far less wear and tear to the laser assembly--thus promoting longer laser life. For the same laser longevity concerns reserve DVD recorders for recording DVDs. Play DVDs on DVD players.
I use Taiyo Yuden 8x Premium Line DVD-R discs for all my archival recordings with my (8) Magnavox, (2) Philips, (1) Pye, (1) Toshiba and (15) Panasonic recorders. One Magnavox HDD/DVD recorder and two of my Philips HDD/DVD recorders have 4x DVD Drives, three of my Magnavox HDD/DVD recorders have 8x DVD Drives and one Magnavox HDD/DVD recorder has a 10x DVD Drive. (Taiyo Yuden bought out JVC's optical media division in late 2008 and has recently added the JVC logo to the existing TY optical media product line. JVC no longer produces optical media. JVC does continue to produce magnetic media.) TY discs may be purchased online. Here is one source:
I use JVC/Taiyo Yuden 16x DVD-R discs with a duplicator or computer DVD burners optimized for higher speed media. These DVD Burners are rated at 20x or 22x but are seldom allowed to burn DVDs at that speed.
I write with some experience. My home-recorded DVD archive is now approaching 7,000 discs. I specialize in films of the 1929-1955 era.