M-audio firewire 410 has pretty good stock pre's
Reading the specs makes me wonder:
2 analog audio input channels
Two independent analog input channels accept a wide variety of input signals. A front-panel switch for each channel selects between 1/4” TS (-10dBV) line-level input on the rear and Neutrik (1/4” TS and balanced XLR) mic/instrument input on the front.So the FW410 has four input jacks, but since you'll have to switch between them, they translate to only two channels. And the FW1814 has only two mic pres, the rest of the channels are line (1/4"). No can do for the OP, then.
Too bad it seems that most gear with more than 2 mic pres (except FTPU) comes in the rack form factor.
A few contenders:
Motu 8pre
PreSonus Firestudio Project
Tascam US-1641
...not to mention even more expensive gear like RME Fireface 800, Phonic Firefly 808, Line6
TonePort UX8 etc...
Some of these racks even require wall power, so check the specs first, if you plan to run them on bus power or battery...
Maybe there are other truly portable interface with 4 mic amps out there, but so far FTPU seems to be the only one?!