I started streaming stuff around the house a few weeks ago, never having any idea how it was done previously. I simply ripped my cds to Flac format (lossless quality) in a program called Musicbee on my laptop. You can then (with a small setup in musicbee) send the music to any DNLA enabled device (such as an amp or bluray player).
You can get someting like this or somilar and turn your amp into a dnla enabled device
https://www.amazon.co.uk/Neet%C2%AE-Wireless-Receiver-wireless-streaming/dp/B00O0U37HO/ref=sr_1_1?ie=UTF8&qid=1477566540&sr=8-1&keywords=dnla+receiver
If your wife has cds, you can make a seperate library in musicbee, or indeed if she has her own computer, put it there. An app such as BubbleUpnp which cost me 4 euro for an android version then allows you to access the music on either computer using your phone or tablet (this is just an extra way and not nessesary, you can stream directly from your computer) and send it to the dnla receiver that is connected to the amp. If you decide to use BubbleUpnp you could just buy a chromecast audio, as this treats the chromecast as a DNLA device, even though it actually works different. It is less complicated than it sounds.Not sure if this helps, but if it interests you I'd be happy to give more info to help you set it up