Can't Control External Monitor Volume Using Sound Interface

Hello Everyone,

I recently purchased an Asus VH238H http://www.newegg.com/Product/Product.aspx?Item=N82E16824236117and connected it to my 15" MBP (Early 2011) via a 3rd party Mini-Display Port to HDMI cable http://www.amazon.com/gp/product/B003OC6LWM/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=486539 851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B0025V2VO0&pf_rd_m=ATVPDKIKX0DE R&pf_rd_r=0C5MTVDY6F5J2FQ1C4FH

So far I have been able to get audio and video through the cable, however I am not able to control the volume of the monitor internal speakers using the volume control lever in the menu bar. (I have to control the volume either within a particular application or use the physical buttons on the front of the monitor)

When I go into audio settings I see the HDMI audio output on the monitor but it says "The selected device has no output controls".

Does anyone know how to enable volume control? I am thinking it may require an additional driver or software patch but have not been able to find anything so far.

Thank you! Any help would be much appreciated!