1880 "legacy" user here. I asked this question a few years back and the answer was kind of expensive. Roland said that if the trim was turned all the way to LINE, that there was no "preamp coloration" on your track. I also heard several others contradict this.
BUT, you still get the halfway crappy Roland A/D converter in the way of your signal. I ended up buying an Apogee Rosetta 2 channel converter and I go from my preamp--->Apogee--->DIGI IN 1 on the back of my 1880. Be sure to set your clock on the Roland to DIGI IN 1, or it won't accept the signal.
I wondered, are the preamps the same on all 8 input channels on the Rolands? I mean the 2 XLRs vs all of the TS inputs? I know the XLRs have phantom power, but don't you get the same gain?