Aha, got it! I just use an XLR to mini-jack cable. Works fine. I've run an EV RE20 directly into the Sony D100 with great results! (Not a very realistic use case, but you get the idea.) I actually use a Beyer M88 as my "studio mic" when I'm traveling as it's pretty small, great sound, and works fantastic with the D100. At any rate the XLR to mini-jack cables I've used worked fine. In fact I notice no discernible difference in "background noise" when using the same mic via D100 versus using my USB Pre2.
Perhaps another key usage difference is I'm almost always using one mic (for ambient sound, for podcasts, etc.). In the case of 2 mics (e.g. 2 people with lapel mics in an interview situation) I use a MixPre with the D100. But that's primarily because I'm both the sound-guy and the interviewer at the same time: I don't have the ability to check levels while recording. The USBPre and the MixPre both have wonderfully effective limiters.
I think if I was doing a lot of 2 mic stuff, I'd go for the SD 702. It would be a much simpler setup. But 90% of the time I'm using one mic, and portability is the crucial factor. If, and when, I use 2 mic setups (and in those cases portability is really not a huge factor) then the USBPre or MixPre, or of course, 702 would be better solutions for me (especially since I always have to do double-duty).
I hope this helps a bit.