I just got a Casio MT-600 and I am in LOVE with the thing. Luckily, it fit the adapter I had lying around from a mostly unused, enormous, Casio CT-640.
It has the same sort of sound as the lower range in the MT series, but it has an ANALOG FILTER! The DCO tones occupy a great sounding transitional space between the MT series of super simple organi-ish tones and the all PCM sample based tones of the CT series that succeeded it.
That means instant classic when combined with an inability to stay in tune, pitchbend, and a really low sample rate, noisy output.
Witness the awesome: MP3
Everything in that mp3 but the drums is completely unmodified MT-600! To get some of the chorus effects I multitracked the same parts with the fine tune knob cranked.
It's not too hot with bass- it doesn't go too low.
I plan to do a mod I found on the interweb that boost the cutoff and resonance limits and brings a control for each out on the front panel. I'm skiddish though, because these are hard to find, and I really like it the way it is. But all these sounds beg for some kind of hands on control.
$2 from a trailer park yardsale.