You can attach a PC or and iPad or iPhone to your amp. They all have low quality DAC contained within . Then depending which device you choose you may need an adapter of some sort. I would take whatever device you choose to the Apple store and let them help you. If you already own the PC or portable device this is the least expensive option.
Sound quality can be improved by upgrading the DAC in the source. The simplest way to do this is to buy a DAC that looks like a usb flash drive that will attach to the source and then attach to the RCA input on the amp.
If you have a component that accepts Bluetooth, AirPlay, or Google Chromecast, then you can send Apple Music wirelessly to that component. I listed the 3 wireless alternatives in ascending levels of sound quality. You will need a DAC, but most have these devices come with an included one. The most common term for these components are streamers, but the terminology for digital can be ambiguous.
I have tried to make this as simple as possible. It can get very complex. I always think that beginners should go slow. However $5K is a healthy budget that can buy a quality set up