The whole purpose of having apreamp is to power the mics and amplify the signal. You don't need mic in if you have a preamp in the chain.
Ordinarily, yes, I understand, you'd run line in. But I was at an acoustic show the other night that was surprisingly low volume. I ran a different set up (DPA4061>battery box (no pre/gain)>R-09, mic in, att -20dB) and even with the gain all the way up on the edirol I was getting just -30 to -20 max during songs. I didn't want to adjust the attentuation to 0 dB for risk of massive distortion during the clapping. In the end, it turned out fine, and I just boosted levels a bit in audacity.
But I wondered if i was running my other set up, the AT's and the ST9100, if I could sorta have 2 stages of gain by running the ST9100 into the mic in of the edirol (isn't the mic in "louder" or more sensitive than line in)? at least it would allow a little more flexibility in getting the levels a little higher. but if i did that, would it significantly affect/color the sound of the recording?
A similar concern about inadequate gain was raised in another thread regarding the low output levels of the nak300s (full body or chopped), and whether the ST9100 had enough gain to get good levels at quiet shows. That also got me thinking about the input for the 9100 and whether it would be (in)appropriate to run the pre into the edirol's mic in to get additional gain. Sure, a pre with more gain would be ideal, but i gots what i gots. . .