Which musical artists are you describing, Eupher? I really would like to listen to someone who could top Josh Groban, because if those people are out there, I'm not hearing them.
I'm not musically trained at all, don't play any instruments like you do, but I do know what I love, and that's his music.
I AM somewhat of a linguist, having majored in French, minored in Spanish, learned kindergarten German by cultural immersion and acquired a smattering of Italian, Hungarian and whatever other language I needed to in order to visit the various European countries. So, on this I feel qualified enough to remark, Josh SOUNDS exactly like a native speaker no matter which language he's singing in. That right there is quite alot of talent. I promise you I certainly would never be mistaken for a native speaker in any language except English. 
Here are a few. Short story on the first YouTube. Laurice Lanier, originally from Jackson, TN, is one of the 3 divas in this clip. She's the contralto. Mrs E discovered her at age 14 at her first voice recital and got her further along in her training at that age. Later, after high school, she had an opportunity to audition at Juilliard and not only kicked butt in the audition, but was asked to sing ALL of her repertoire. She won a full-ride scholarship to that very distinguished school. You'll likely not hear much of Laurice, even though she's every bit the classically-trained singer WITH PIPES (Groban doesn't have a very good instrument, imho), and with talent, than you'll ever see. Laurice didn't want to sing just opera, and preferred to abstain from that "world" in favor of what she's doing today.
Laurice would've sung at our wedding, but she was in NY at the time and couldn't make it.
[youtube=425,350]http://www.youtube.com/watch?v=Sq_092C_drE&feature=related[/youtube]
Here's another gal who crosses over from opera to popular music. Dawn Upshaw.
[youtube=425,350]http://www.youtube.com/watch?v=VDpNJgu7aWE[/youtube]
And here is a well-known ensemble in England, but probably unknown here. They're called The King's Singers. They sing
a capella, and are known for not just their "sung" voices, but sounds in all sorts of settings, including humor. This is probably a good example of their renaissance-era stuff. Intonation is perfect, diction is even better, and their dynamic control is simply amazing.
[youtube=425,350]http://www.youtube.com/watch?v=5kXnfPu1-1w&NR=1&feature=fvwp[/youtube]