I too, tip my Pi's back with a 3/4" block of wood under the front edge. You might try the mod to the paramours that Paul Joppa suggested: http://www.audioasylum.com/forums/pi/messages/4033.html
It seemed to enhance the high end performance of my Pi's. I'm still not sure about all aspects of this change. Recently, there has been a surge of EMI/RFI noise in my neighborhood which virtually precludes listening to my system on most days! Damn!

G.

• http://www.AudioRoundTable.com/PiSpeakers/messages/4033.html