sound like what you need is an RME fireface.
4 decent preamps, really good converters, zero latency monitoring and the great totalmix software.
you'll have to buy used if you wanna stay within that budget though.
another option would be the focusrite octopre LE with the digital option, 8 very decent preamps (better than the ones on the RME IMO), decent converters (not as good as the RME but definitely very usuable). you'll need a way to get ADAT into your computer though