I know we are still way off topic, but I have to chime in with my reason for using outboard preamps. Ultimately it comes down to functionality for me, regardless of quality difference. I always make better recordings using outboard preamps than not.
Early in my concert taping career I ran a multi-mic rig with a mixer during a time when almost nobody used anything between mics and recorder, except battery phantom boxes that guys running condensers had. Back then I discovered a huge value being able to harness the signal ahead of the recorder. I liked how the sensitivity of the gain pot on the recorder was eased by taking line-in.
Every portable recorder I have ever owned since, cassette, DAT, solid state, has had an input gain sweet spot range where the deck performed best. For myself, I have been unable to find a better way to keep the level of the signal to the recorder's line-in within that range than using an outboard preamp. For this reason I expect I will always use outboard preamps.....