ArcGIS Reference Layer over ArcGIS Terrain base(or Imagery) Layer using OpenLayers

Question

I am using Openlayers for a Map application which uses basemaps by ESRI (or ArcGIS). What I am trying to achieve is something like this: http://www.arcgis.com/home/webmap/viewer.html From Basemaps select Terrain with labels.

Here is what I am doing:

arcgis_world_ref_overlay   = new OpenLayers.Layer.ArcGIS93Rest( "World Overlay Reference",
                                   "http://services.arcgisonline.com/ArcGIS/rest/services/Reference/World_Reference_Overlay/MapServer/export",
                                    {layers: "1",TRANSPARENT: true},{isBaseLayer: false,opacity: 0.5, displayInLayerSwitcher: false, visibility: false});

arcgis_terrain  = new OpenLayers.Layer.ArcGIS93Rest("World Terrain Base", // name for display in LayerSwitcher
        "http://services.arcgisonline.com/ArcGIS/rest/services/World_Terrain_Base/MapServer/export", // service endpoint
        {layers: "0", format: 'PNG24', sphericalMercator: true});

Attached is the output I am getting:

This is the desired output (uses Dojo and cached tiles but same service):

What am I doing wrong here?

Any help is greatly appreciated.

Thanks in advance.