Probably the FiiO M6. I say probably but I never tried it. Amazon Music is on the whitelist of apps but you can also sideload apps turning on the Dev Options. I installed standalone version of PowerAMP on mine, which worked fine. It’s not the most powerful device though so how well the M6 would handle Amazon Music I can’t say. Wifi is only 2.4GHz may not be an issue for you. It’s also 3.5mm SE only if that bothers you at all.
No hard sell, I still have mine for sale - PM if you’re interested. If not, no worries.
Edit: link to my post on the Buy/Sell thread for some pix Buy/Sell and Looking for Thread - #2311 by saltire