can you sample into a mpc 2000xl directly through rcas like you can on the 404'?

You need a preamp, also I don't believe it has RCA's (TS 1/4 or whatever). That said a lot of new turntables have built in preamps (Numark PT-01, etc)

running it through a mixer then?

same as the 404- if your turntable signal needs to be boosted, then you need a mixer or amp

yes u can, exact same as the 404 but u need the 1/4 rca's.

n obvously youll need a preamp or a mixer for your tunrtable to boost the signal