Check out the Harmon Kardon DRP series. As best I can tell, it's a switching amplifier where you modulate the switching frequency via Pulse Width Modulated wafeform, thus changing the gain???

http://www.harmankardon.com/product_detail.asp?cat=REC&prod=DPR%201001&sType=C

Best part about switching supplies is that they are very efficient (80-90 pct vs ~50 percent for a linear supply), and thus can be small and light (i.e. no heat sinks)

-Ted