re: 20/18/16 truncating
If you go back a few threads, Rick Koch tests passing 24bit data through the Korg. It appears results would give "20 in is 20 out".
re: scary algorithms
If you fear artifacts then do a software re-sample to double the bit rate of your master pair. Bring it up to 96khz. That will place a linear interpolated sample point between existing samples.. Dither this to 44.1khz. If you think this would cause a problem then imho it is the same problem everybody doing 24/96 is facing.
re: Marantz CD burner
Brad I know you have been burning CDs through the SPDIF at 48khz and letting the Marantz massage them.. How does it sound?