@martinman There may be a couple variables in your system causing the DACs you've auditioned to sound very similar. What are you using to stream Amazon Music? If a computer, then a general purpose computer will never sound as good as a good quality purpose built streamer, especially if you use a USB cable from a computer to your HINT 6 integrated. What's the quality of your Internet network in your home? Make sure you're not using WiFi for Amazon Music playback and use good quality Ethernet cables. I recently added an EtherREGEN device to my home network that feeds my Streamer/DAC and was amazed at the SQ improvement.
It will help if you can isolate everything in your system used to play Amazon Music. One way to do this is to get access to a decent CD player preferably connected to your HINT 6 via XLR cables. Select a Redbook CD you're very familiar with. Then look for the same album on Amazon Music at Redbook CD resolution and compare the SQ. In most cases, the SQ of the local CD will sound better but it should be a close fight. If you find that the local CD is noticeably better, then use the free 14-day Qobuz trial as many on this forum have suggested. This will help you compare Amazon Music to Qobuz. If you still find the local CD sounds better, then it's likely the computer or USB cable or both that are your weak links in the chain.