I just wanted to say, these are fantastic. AA has always been my favorite hero, so I've been waiting (no so) patiently for IR to hit, and I gotta say, having all the Instruments (and his voice) with their own custom sound effects is just freaking awesome. Kudos.
Have you taken a look to see who the voice of Argent is?
Is it Gilbert Gottfried?
I like the Adept's sound effects as well. I do hope he remains unique in that aspect.
Edit: Though I could see an exception of Guise uses I Can Do That Too and use's the Argent Adept's vocalize. Which makes me wonder as well if the variant Adepts will have different sound effects for their base power. I certainly would hope so.
Maybe I'm unique in that I don't like his sound effects, I have to turn them off. While the voice in perform isn't a bad voice, it isn't the trained operatic voice I imagine him to have. And the bell... doesn't sound like a bell anyone could play a harmony with. Some of the sounds I can almost imagine are the beginning of one of his epic songs that inspires the heroes, but the bell and his voice just completely fall flat for me.
I'd be surprised if AA had a trained operatic voice - the bio indicates that Drake was a bartender before he became the Adept.
I'd also add that Handelabra has GtG listen to and approve the music used for the game. So I'd find it odd if Christopher or Adam didn't approve the sound effects used for the Argent Adept.
I will add, though, that I also dislike the bell's sound effect. But that's because I have a strong preference for Deep, booming church bells, probably caused by too much time spent reading Redwall and Sabriel as a child.
I posit there is no such thing as too much time spent reading Redwall and Sabriel. I enjoy the effects, for what's it worth. They were a nice surprise.
I recognised the voice right away.
Who's is it? It's a good voice, high tenor, and was able to pull off a little bit of vibrato at the end of the aria.
While it does sound similar, I don't think it's who you think it is. 
(For those who don't know, you can go to the Credits from the Main Menu, scroll down, and see their name.)