Querying Amazon Product API to get ASIN of MP3 download using artist and title

I am new using Amazon's Product Advertising API, and for my first project with it, I am trying to get the ASIN of the MP3 download product of a particular song, based on the artist and title. I will eventually be using these ASINs to populate an Amazon MP3 Clips Widget.

I am using the PHP class from CodeDiesel.com to get started. It works just fine, and I have added the following function:

    public function searchMusic($artist, $title) {
        $parameters = array("Operation"     => "ItemSearch",
                            "Artist"        => $artist,
                            "Title"         => $title,
                            "SearchIndex"   => "Music",
                            "ResponseGroup" => "Medium");
        $xml_response=$this->queryAmazon($parameters);
        return $xml_response;
    }

Now, the trouble is, I can only seem to get albums this way. For instance, if I put in "Robert Randolph" for the artist, and "Colorblind" for the title, I get Robert Randolph and the Family Band's Colorblind album. If I search for a particular track, such as "Thrill Of It", Amazon can't find anything.

So what I need to do is first figure out how to make a query for track title. Then I need to figure out how to limit my results to just MP3 downloads. How can I do this?

If there is documentation on the topic, can you point me in the right direction? I have been reading through it, but don't see any parameters for what I want.

Thank you for your time.