The TX816 is a 4 unit high rack which houses a power supply and eight TF1 modules. Each module IS an independent DX7 with 16 note polyphony.
This means that you have the possiblity of 128 note poly, and eight part multitimbrality.
Each module has it's own midi in/out socket and XLR audio output. There is no stereo master output, so you'll have to think seriously as to whether this synth is for you.
The sounds are glorious when layered. Yamaha provided factory patches which showed of the synth as a multitimbral sound module, and also composite patches where each module represented a different aspect of a sound.
Well cool, and in my opinion, seriously underrated.
I have the original factory sounds, so if you're interested, just e-mail me!