The output taps are very similar to the gear ratios on your auto transmission . . . in this case, how fast you can go depends on the balance of how high the engine redline is, and how steep a hill you're going up.
If you correlate maximum audio power to maximum vehicle speed, then the amplifier's internal power-supply voltage is like the engine redline, and how steep the hill is correlates to how much current the speaker is drawing (the impedance). The usual penalty for "lugging the engine" (being on a higher-impedance amplifier tap) is an increase in distortion, and sometimes a modification of bandwidth and transient response. The penalty for being on a lower-impedance tap is a reduction in gain and power output, but if the amp is operating in a more linear fashion, it may still sound more powerful.
While I'm not familiar with the Cellos in particular, most dynamic speakers require more current (and power) in the bass range. The only thing to keep in mind if you're going to use different amplifier taps for the bass and mids/highs is that the gain will be different, so you'll have to turn down the mid/high amp a bit to get the same balance.
Also, you shouldn't use more than one tap on a single amplifier channel at one time. While there are some hypothetical situations where this could kinda work, it will most likely cause a very demanding load on the amplifier, and adversely affect the damping/HF performance of the output transformer/autoformer.
