Why am I suspicious of the Zoom mic pres? Maybe they are fine for voice, but I would like to hear comparisons with the 788t or this 888 when it comes to music.
The specs are a bit better on the 888 and SD uses class A discrete pres designed in-house in contrast to the chip-based pres that I think Zoom uses. Unfortunately, Zoom doesn't specify noise. I doubt there would be much audible difference in most cases, although they may have some more subjective difference in how they sound. It would be nice to hear a well controlled comp.
In any event, I don't think it is an "apples-to-apples" comparison between the 888 and the Zoom F4/6/8n, or any other "prosumer" recorder (like the MixPre series), as the 888 has a ton of extra features. It also costs an order of magnitude more...