Here's what I ended up doing. I bought four things, an Apple Airport Extreme, an Apple Airport Express, A digital audio optical cable, and a 3 TB GDrive. Apple is very smart, and very annoying, because the Express ($99) will hook up to my stereo receiver, but will not hook up to the hard drive. The Extreme will not hook up to the stereo, but will hook up to the hard drive. I can use both to extend my existing wifi network, so that's ok, but I could do without the Extreme if I hooked the hard drive into my computer instead of through the wifi. Like I said, I can use the wifi extension anyway.
There is one really cool thing about the Express. It has a mini plug output, like the headphone jack on an IPhone, but is can work as a digital output if you buy the right cable and your receiver can accept a optical digital input. If it can't, you can use a standard mini to RCA plugs splitter.
I can now control what plays through the stereo with my IPhone. Sweet. And it sounds terrific.