If I understand correctly, you want a synth module to connect the keyboard to? And the synth should have a sequencer on board, and be able to play chords (ie not monophonic)?
Some of the Roland boutiques might fit the bill, eg the SH-01A or the D-05. But I think it largely depends on what features & sounds you want from the synth. The Korg Minilogue XD is a bit bigger and more expensive but another option.
If I understand correctly, you want a synth module to connect the keyboard to? And the synth should have a sequencer on board, and be able to play chords (ie not monophonic)?
Some of the Roland boutiques might fit the bill, eg the SH-01A or the D-05. But I think it largely depends on what features & sounds you want from the synth. The Korg Minilogue XD is a bit bigger and more expensive but another option.