The tape output does not lose low frequency data - its signal is split off prior to the processing. That's probably the main reason that the digital input didn't yield a tape record output - the signal sent to the tape output is taken from a point upstream of the digital processing (before the analog is converted), and at that point in the process there's no analog signal available if a digital input is being used.

I see now what you're doing, nfaguys, and it's also a good option - if you have a single source that you plan to record from, hook it directly to the recorder. I actually started doing this myself lately, although I haven't used it yet (the stereo analog and s-video output of my HD cable box go to the DVD recorder while the digital audio and component video from the HD box go to the 990).