Seems a shame to dump a couple of really nice keyboards to get mp3 playback...
Wouldn't an MP3 player do that at considerably less cost?
Or why not a nice arranger? Most can easily keep up with a stage piano in 76 form. In this price range, you need 76, I'd take a good look at an E-60. No, it won't do MP3, but that's easy with an mp3 player. But you DO get a full arranger, which if you are in a duo or trio without rhythm section gives you FAR more opportunity to go 'off the page' than an mp3.
JMO...
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An arranger is just a tool. What matters is what you build with it..!