Hi Paul

You "might" consider a Yamaha 9000Pro. Almost all arranger keyboards are ROMplers, in that the generate sounds using pre-recorded waveforms. This is the polar opposite of what your .com would do. The 9000Pro is modular in a couple of senses. First of all, you can add plug-in boards to access non-Rompler synthesis methods like Analog modeling, Physical modeling, and FM. Second, if you get the analog modeling synth, I think it emulates an analog modeling synth. While the 9000Pro doesn't have many knobs, you can add an external know bank to control parameters directly.

You should also consider getting a .com synth and an arranger. They certainly would not be redundant, they are completely different instruments. If money is limited, get an inexpensive arranger just to see what it can do.