I took the Voice Prism out twice this week, and after very little tweaking, I managed to get the same performance as I was used to with my Digitech unit. (Vocalist access) Here are the improvements:

NOISE -
There ISN'T any !!!! It much, much cleaner. Night & day.

EFFECTS -
First off, there are several, and they are super high quality (Typical for TC Electronics gear). I can layer reverb and delay and still use a dedicated EQ, gate & compressor. You can also tell the effects to process the Lead, the Harmonies or both.

VOICES -
much more control over blend, gender, and such. Really nice to have. Easy to set up 4 knobs to be dedicated to "whatever" you need too. You can have level, pan, gender, effects - all modifiable at the touch (turn) of a knob in real time!

AUDIO IN -
better than the Digitech again, because you have control over how much of each effect the aux signal gets sent to.

48v -
Powers condenser mics. Great feature, especially for studio use. It's a very quiet preamp too. There is an On/Off switch for the harmonies, the effects, and even the mic signal! All dedicated buttons.(Not available on the Digitech)

SOUND -
It's not WORLDS better than the Digitech, but it IS worlds quieter, and that is definatly worth the extra money. Add up the extra effects, the phantom power, the real-time knobs, and the crystal clear sound - it's a great buy, even if it IS close to a thousand bucks.

I passed on the expansion board - I need to hear what it offers before I sink another $400 into something. From what I read, and other opinions - it may not hold a place in MY future.

In short, this is a terrific harmonizer. It's also a terrific effects processor even if you only need it for a PA mixer. It packs a whollap, and it's pretty too. It's not for the average, casual user because of the price, but after you hear it .......... it's tough to go backwards again.
My Yamaha goes "hisssssssssssssssssss"

The TC goes .............................................................................................