JavaScriptを使ってみませんwindow.locationか？

<div id="advancesearch">
    <div class="audio-quicksearch">
          <select>
             <option value="Microphones" onclick="window.location='http://www.google.com'">Microphones</option>
             <option value=""></option>
             <option value=""></option>
             <option value=""></option>
           </select>
      </div>
 </div>

または関数を作成します

<div id="advancesearch">
   <div class="audio-quicksearch">
         <select>
            <option></option>
            <option value="Microphones" onclick="redirect_me('http://www.google.com');">Microphones</option>
            <option value=""></option>
            <option value=""></option>
            <option value=""></option>
          </select>
     </div>
</div>
<script>
   function redirect_me(re_link) {
   window.location = re_link;
   }
</script>