How to insert formatted HTML into editor from custom plugin?

Using 4.1rc.

I want to create a custom plugin that inserts an object element:

<object width="300" height="42">
<param name="src" value="/mypath/my.mp3">
<param name="autoplay" value="false">
<param name="controller" value="true">
<param name="bgcolor" value="#FFFFFF">
<embed src="/mypath/my.mp3" autostart="false" loop="false" width="300" height="42" controller="true" bgcolor="#FFFFFF">
</object>

I have created a custom plugin which with the onOk function includes the following:

var dialog = this;
var srcURL = dialog.getValueOf( 'tab-basic', 'srcURL' );
var mp3Object = editor.document.createElement( 'object' );
var mp3param = editor.document.createElement( 'param' );
mp3Object.setAttribute( 'width', '300' );
mp3Object.setAttribute( 'height', '42' );
mp3Object.appendChild( mp3param );
mp3param.setAttribute( 'src', srcURL );
editor.insertElement( mp3Object );

But this logs the error:

Object #<Object> has no method 'appendChild'

If I try to create the html manually I also get an error:

var mp3Object = '<object width="300" height="42">';
mp3Object += '<param name="src" value="' + srcURL + '">';
mp3Object += '<param name="autoplay" value="false">';
mp3Object += '<param name="controller" value="true">';
mp3Object += '<param name="bgcolor" value="#FFFFFF">';
mp3Object += '<embed src="' + srcURL + '" autostart="false" loop="false" width="300" height="42" controller="true" bgcolor="#FFFFFF">';
mp3Object += '</object>';
editor.insertElement( mp3Object );

How can I insert html into the editor or params into my object to allow me to insert the string I need?

Thanks!