I have been exploring the same issue (and am also surprised how little information I have been able to find about how to do this).
If you are willing to purchase a new receiver, Yamaha released two new receivers this fall that are advertised as featuring "web browser control." A home audio/theater installer I spoke with told me that these receivers can be controlled over a home network, either hard wired or wireless. I visited the Yamaha user forum recently and there were a few posts from people who apparently are successfully using this feature to control their receivers with an iTouch. (I have no personal experience with these products yet. I not aware of any other receivers that have this feature, but would expect other manufacturers to offer this same ability in the near future given the apparently increasingly popularity of digital audio servers.)
Wayne
