Hey Phil,
you've been given some excelent advice here on bit depth. I'll even go so far as to say, no matter the sample frequency, NEVER record at less than 24 bit! I generaly record at 24/48, but 24/44 is ok too. I use R-09's. (I have 5 of them) I may start moving to R-05's specificly for the ability at record at sample rates. I just need to wait until I find out how good the pre's in them are. What I might suggest is doing some tests with a lour stereo and compare the settings on the D-8 to the settings on the R-05 at say, -20dB. (Depending on how loud your stereo actualy is.) It's not 100% conclusive, but it's going to get you in the ballpark. Or, using the line out from your computer as was suggested and switching between decks to get an idea what's going to happen at different settings. I know the unity setting is quite different between the 09 and the 09HR, so there's every possibility they'll be different again with the advent of the 05.
I'll be looking forward to seeing more in this thread! Thanks for posting it.
-JT