For DirecTV, you should order the DirecTivo
from DirecTV. It's either $49 or $99, depending on their current promotion, and includes free installation.
Note this box won't record HDTV, but it will let you watch one SD channel while recording another. It will also let you record two different SD channels simultaneously while you are watching a previous recording. Of course, you can pause, instant replay, and rewind live programming, and skip commercials on recorded programming. It's very, very easy to use.
The HDTV DirecTivo
is much more expensive -- at $899 -- but it lets you record any two HDTV (or SD) channels simultaneously while watching a previous HDTV recording. It has two OTA tuners and two DirecTV satellite tuners built-in, so it would eliminate the need for your current HDTV receiver. There is no way to record HDTV from your current DirecTV receiver; in order to record HDTV, the HDTV receiver must be built into the DVR, as in the case of the HDTV DirecTivo
With both the standard DirecTivo and HDTV DirecTivo, recordings are 100% identical to the original live broadcast, because it records the digital bitstream directly from satellite (or the digital bitstream from your local DTV/HDTV broadcaster). There's no PQ degradation and you retain the Dolby Digital sound.
The DVR fee for the DirecTivo
is a flat $5/mo, regardless of how many of them you have in your home. They waive the fee entirely if you subscribe to their top programming package.