Glad to see someone else was interested in this too.
I ended up buying a first gen airport express to go with my HTPC, the ipad and another airport express.
I had to hardwire the first gen airport express (~$40 on ebay if I remember correctly, much less than a current gen) to a Windows XP computer to get it to update the firmware, I couldn't do it wirelessly or from a Windows 7 computer for some reason.
Once I did that, I had all my devices on the wireless network in the house. I connected my various speakers/receivers then I used a combination of the following:
Spotify running on my desktop computer
Spotimote server running on my desktop computer
Airfoil for Windows on my desktop computer
Airfoil Speakers for windows on my HTPC (acts as an Airplay receiver like the airport expresses do)
Spotimote for my Android
It turns out Airfoil didn't support my sound card but once I switched to the integrated audio on the motherboard, it worked perfectly. Using this setup, I could stream spotify sync'd to all my airplay devices and control the spotify client on my desktop computer via my Android. Spotimote wasn't perfect, I had to restart the Android app a lot but it did the job. Everything else worked great. I ended up buying a license for Airplay so my total cost was $65 or so to get what I needed.