Sony's refresh of its DVD recorder line--on display at its product showcase in Las Vegas--reflects the new FCC mandate to include a digital ATSC tuner in newly introduced recording devices.
In keeping with the trend at this year's Consumer Electronics Show, the four recorders are broken into two categories: those with no tuner, and those with ATSC tuner. An ATSC tuner adds some additional cost to the DVD recorder, which is why vendors are giving you the choice--especially considering you may already be relying on your cable box's tuner, regardless. (The pricing wasn't announced)
Sony showed two tuner-less models. The RDR-GXD355 has line-input recording (for use with a cable box) and cable-box pass-through, so you don't have to have the unit on order to access your cable box's channels. The RDR-VX555 builds on the RDR-GXD355's features by adding a VCR with a DVD recorder, and providing one-touch bi-directional dubbing between VHS and DVD.
The other two models on display each featured an ATSC tuner. The RDR-GXD455 can record to double-layer DVD+R discs, while the RDR-VXD655 also offers bi-directional dubbing between VHS and DVD.
Unfortunately, you can't record in high-definition to standard-definition DVDs. The unit will only record in standard definition, down-converting the image from the high-def feed the ATSC tuner will receive.
All of the models feature HDMI output and upscaling of standard definition video to 720p or 1080i.