Check out the BBE Acoustimax preamp:http://www.bbesound.com/products/stomp_boxes/Acoustimax/index.asp
I was debating about whether to go with the Major Key Harmonic Clarifier or an external box, and decided on the Acoustimax instead. The BBE rep wasn't sure when I asked him if the Harmonic Clarifier had a "better" (more Rhodes-specific) tuning than the Acoustimax preamp, but the thinking was that it was probably the same.
Here's why I went with the Acoustimax instead:
1) Small, well-built;
2) More tone controls than the Clarifier. The Acoustimax has EQ with bass, treble, mid (with notch/frequency settings) -- in addition to the familiar BBE process and low end controls;
3) Acoustimax will work as a preamp for your Rhodes with the BBE enabled or disabled. Turn BBE on or off during performance as needed....
4) Acoustimax has an XLR (direct) out, in addition to 1/4" outs. Both outputs can be used at the same time -- XLR for the house, 1/4" for your stage amp.
5) No batteries (although the Acoustimax does need a wall wart
6) Acoustimax can be used for other things (acoustic guitars, for example, or other acoustic or passive electric instruments) -- so it's more flexible
7) No need to modify (drill, etc.) your increasingly rare vintage Rhodes.
8 ) Acoustimax cost, at just under $200, is comparable to the Major Key Harmonic Clarifier, but to me offered more flexibility.
9) Acoustimax BBE chip is confirmed to be the 4th generation (higher resolution) chip. Not sure what the Harmonic Clarifier chip is (could be third or possibly fourth generation).
10) included mute switch -- for tuning or just cutting sound output for whatever reason.
The only downside is that the Acoustimax isn't built in, so it's another box to haul along. The nice thing is that the box is fairly small, is made of durable metal, and can be placed either on top of the Rhodes or on the floor underneath it.