Can't get custom JSONP pipeline to work - php

Question

I'm building an audio player that makes 3 different API calls, and I need them all to be in JSONP format, so I made a PHP proxy file that determines the output of the JSON data like so:
$datatype = $_GET["type"];
$artist = urlencode($_GET["artist"]);
$album = urlencode($_GET["album"]);
$content = "";
if($datatype == 'albumart'){
$content = file_get_contents('http://ws.audioscrobbler.com/2.0/?method=album.getinfo&api_key=037358e302c80571663e6a7a66b1dc05&artist=' . $artist . '&album=' . $album . '&format=json');
} elseif($datatype == 'artistart'){
$content = file_get_contents('http://ws.audioscrobbler.com/2.0/?method=artist.getinfo&api_key=037358e302c80571663e6a7a66b1dc05&artist=' . $artist . '&autocorrect=1&format=json');
} else {
$content = file_get_contents('http://cjzn.streamon.fm/metadata/recentevents/CJZN-48k.json');
}
header('Content-type: application/json; charset=utf-8');
echo $_GET['callback'] . '(' . json_encode($content) . ')';
Upon testing the output it seems to work fine, it gets the respective API data, wraps it in the JSONP () and accepts a JSONP callback.
Bur when I try and use it in my Javascript file it doesn't seem to work, but I can't figure out why! Here's an example of one of the functions being used to call the JSON data:
function getAlbumArt(artist,album){
var dataArtist = artist,
dataAlbum = album,
albumArtURL;
$.ajax({
url: 'jsonproxy.php',
dataType: 'jsonp',
data: {
type: 'albumart',
artist: dataArtist,
album: dataAlbum
},
success: function(data) {
if(data.album.image[4]["#text"]){
var albumArtURL = data.album.image[4]["#text"];
$('section.player div.album-artwork').css({'background-image':'url("' + albumArtURL + '")'});
} else {
getArtistArt(dataArtist);
}
},
error: function() {
getArtistArt(dataArtist);
alert('Sorry, unable to retrieve album artwork!');
}
});
}
Can anyone help with why this doesn't work for me?
Edit
I did alert(data); on success, and that returned all of the data from the feed, after that if I did something more specific like alert(data.album.image[4]["#text"]); it returned undefined. Very confused here. Anyone have any thoughts?