The Trident is 8 voices polyphonic and it has 3 sections.
However, if you split two sections, you will still only be able to play 8 notes at a time.
From the schematics in the Technical Manual, I would say the synth and string section are polyphonic, but unfortunately the Brass one is paraphonic...
If that one wasn't paraphonic, the Trident would have been even better.
The overall sound is really nice, it's just a shame it doesn't have all those mood routings (in fact, it only has envelopes and PWM... nothing more...).
The MkII is definitely the one to get, due to real memories and extra envelope, but if you have the chance of getting an MkI, I would say go for it, as it is still an amazing machine.
By the way, the keyboard is way better than the one in the Polysix, and I think the overall sound is better too (I only got around 48 hours before the manual mode of synth section started to freak out... but I think it just needs a cleaning inside...), but unfortunately it doesn't have the wonderful unison mode you get on the Polysix, which is the reason why I am keeping that one.