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 .............................................................................................

Glad to hear an expert confirm my impressions. I paid $800 for a new unit by keeping an eye on ebay. I really like the combo LED/LCD display--the LED has numbers you can read from far away, while the LCD provides detailed information--including cute humanoid icons to indicate the harmony voicings.

Too bad the aux in is Mono. I wish it were stereo. If it were, I could plug my Karma into it and avoid using a mixer. My Roland KC-300 have multiple ins, but then I have no stereo headphone mix. So I have to add a mixer.

BTW: There is now a software vocal harmony plug-in for Cubase VST called "voice machine" made under license from TC-Helicon.

That AUX in is a lifesaver, and why I bought the Digitech a few years ago. To add the harmonizer to my rack, I had to loose a space that used to house an effects unit. Now, other mics or instruments can share the same great effects that MY voice has on it !
I have it in a three space rackbag with a TOA single space stereo mixer. Smallest, hippest PA bag in town !