It's not as easy as you make it sound. I have PSR 2000 and KORG D16.

There are no Hardware Audio sequencers out there, except the one by Tascam, i don't know which model, but it's like $4000.

There are Hard Disk Recorders. The Zoom multitrack recorder is just a linear hard disk recorder. And there ARE 4 tracks, that means you can play 4 tracks. That is 2 stereo tracks. You can switch between virtual tracks, but I don't think you can do that in real time.

The main benefit of arranger keyboard is the live performance feature. You can't get that with hard disk recorder.

Also, YAMAHA PSRs have the most number of DSPs among arrangers. No other arranger offers EQ for each MIDI channel.

So, before you buy that multitrack, think about it again.