yes the model C is basically taking the output signal of the guitar and converting it into physical vibration, i'm assuming through some kind of cone-less loudspeaker (a magnet, a very heavy voice coil and a spider). but what i'd be doing, rather than attaching it to the guitar, is attaching it to, say, a zither or harp. if tuned correctly, the strings on the zither/harp should be induced to vibrate sympathetically with the notes played on the guitar. the zither/harp strings can then be amplified and played through a secondary speaker.
OR the sympathetic strings can be induced to vibrate by an electromagnetic sustainer, which is basically a pickup run in reverse (although apparently you can't use a regular pickup, it will burn out). this probably would work but it's a much more artificial sound (like the E-bow, if anyone's familiar with that).
now if i had a spare $279 to spend, i'd probably go ahead and buy the model C; but, i don't. i'm wondering if i can duplicate this myself, for cheaper.