How do I change my iTunes URL

The elegant way would be to fit the something like this
‘
<itunes:new-feed-url>the URL of the new feed location</itunes:new-feed-url>
‘
into the XML code of your old feed (see also http://www.apple.com/itunes/podcasts/specs.html#newfeed and http://www.apple.com/itunes/podcasts/specs.html#changing).

The question is probably how to do this. If you craft this feed by hand then you can paste this line of code into the <channel> section of the feed.
If you use a CMS like WordPress at the old location then you could search for a plugin like podPress which has a setting where you can insert the new feed location and which adds the XML code automatically at right place in the feed.

Once this tag and the new URL is in the code of the old feed the iTunes server will update its information and look after a couple of days at the new location for the feed.

Go to the podPress > Feed/iTunes Settings page, section “Settings for the default Feeds”. There you can find the setting “iTunes:New-Feed-Url”. Enable it and insert the new URL.
This will insert the required meta tag also into the XML code of the custom post type feeds.

Will the above change affect all my manually submitted URLs to iTunes?

Yes. The method I tired explain would only be usable in a case where you would want to redirect one single feed. Because the setting on the podPress > Feed/iTunes Settings page, section “Settings for the default Feeds” would set in all custom post type feeds the itunes:new-feed-url tag. But it is not possible to set different URLs for all the different feeds.

How do I get them to point to this new server?

Well, you could you a further custom code snippet:

add_action('rss2_head', 'pff_modify_rss2_head');
function pff_modify_rss2_head() {
	if ( 'audio' === get_query_var('post_type') ) {
		$term_data = get_term_by('slug', get_query_var('speaker'), 'speaker');
		Switch ($term_data->name) {
			case 'John 1' :
				echo "\t".'<itunes:new-feed-url>http://example.com/john1</itunes:new-feed-url>'."\n";
			break;
			case 'John 2' :
				echo "\t".'<itunes:new-feed-url>http://example.com/john2</itunes:new-feed-url>'."\n";
			break;
			case 'John 3' :
				echo "\t".'<itunes:new-feed-url>http://example.com/john3</itunes:new-feed-url>'."\n";
			break;
		}
	}
}

This is an example. If you use this code snippet then it is necessary that you adjust the case 'john3' : lines. Instead of johnx write the names of the speakers and adjust the values of the new feed URLs.
If you have more than 3 speakers, copy one of the

case 'John 3' :
	echo "\t".'<itunes:new-feed-url>http://example.com/john3</itunes:new-feed-url>'."\n";
break;

and paste it is often as you like.

If had enabled the new-feed-url option on the Feed/iTunes settings page then disable it. (This code has collision control and would print simply a further <itunes:new-feed-url> tag. That could confuse the iTunes server.)

Oh, I have not controlled the output of my last post. But I guess you have guessed that the solution would be the numeric equivalent of the ampersand. & #38; (without the white space between the first two characters)