I suggest a Tyros, though as you say that you are looking for at least 76 keys then a 9000 pro might be the nearest choice...
If you need more powerful sequencing onboard features and don't need styles, go for a big Roland or Korg workstation.
Otherwise buy an 88 note midi controller keyboard and hook it up to say an SC8850 or its replacement module and a PC sequencer.

S.

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