I use a SD302 in front of a DR-100 and it works great, plenty of gain. I believe the audio circuits on the MixPre are the same as the 302, it just has less features, so you should be good. Use XLR out on the SD and XLR in on the DR-100, at line level.
Good luck,
Grant
Good luck,
Grant
I have had mixed results sending line level from my Alphamix to the DR-100's XLR inputs, and found repeatable, very good results feeding the 1/8" stereo line in on the DR-100 from the 1/8" transcription output of the Alphamix. For what you're going to spend on the DR-100 and the Mixpre, you might be better off with a Edirol R-44 alone, and then later, when budget allows, add a used SD442 in front.
Perhaps other can comment about whether the Edirol has enough gain to get sufficient level from something like the Rode NTG-2 or 3.
Don't get me wrong, I like my DR-100 and kept it after purchasing the 680, but interfacing from a mixer to the line inputs on the DR-100 may complicate things.