I use this system from Monoprice. Works well and has an app for it. Did the installation myself since my house was also pre-wired. It can stream 6 different audio sources to 6 different zones, though I've only ever had three sources active at any time.
This definitely comes in much cheaper than both the systems you had listed. Actually it looks like the Casa one is just a rebranded monoprice with the music storage included.
https://www.monoprice.com/product?p_id=10761