Sometimes, too much equalization can be problematic for a Rhodes piano. The first thing to check is the tine to pickup distance. This distance, in general, should be minimized, which means keeping it between about .032" (.75mm) and .070" (1.25mm). Also the height of the tine in relation to the pickup must be adjusted. You can find all this information here
http://www.fenderrhodes.com/service/manual.html. Hammer tips can be problematic if they have grooves worn into them.
If you have access to a graphic equalizer, dropping the gain a bit in the region of about 200 Hz to 400 Hz can often take lots of muddiness out of the tone. Too much treble boost can be a problem, however, because it can make the high notes too loud, which will then necessitate backing off the pickups, which will produce a tone with fewer harmonics. If you have a graphic equalizer, increasing gain above 3 kHz can add a bit of brightness.
One nice thing about Rhodes pianos is that they are quite adjustable. I'm sure you can improve your tone with some fussing around. However, don't expect too much brightness out of a Rhodes--its' not part of its DNA.