The mic pre’s are more than serviceable. None of these kinds of units are going to be sporting Avalon pre’s anyway. If you did want to do that, you could still put your own mic pre in the chain before the HD and just not run phantom power from the HD, no biggie.
I wouldn’t worry about the A/D D/A converters. At this level that’s the last thing in the signal chain that would make any kind of noticeable difference.
For reference, here’s a song of my friend’s that we recorded - we recorded all the tracks on the HD (Zoom R24) using the onboard mic pre’s (used AT2020, SM57, and some Behringer C2’s for the acoustic gtr for mics). I took all the tracks and just put them into Cubase to mix, etc. Some reverb and a few other effects were added in Cubase.