Well, as I said your system is pretty well balance. Given your budget it would be easy to invest it and simple exchange one pretty good sound with a different pretty good sound. So, I had two paths.
I think to increase the sound quality I would not invest any more in PC/Data clean up. When you decide you want to move up in sound quality on the front end, then go to a dedicated streamer. Maybe something like a used Aurender N100… or better yet N200. So, I guess that is my first thought. If you want to improve the front end… you should spend more. So, if you want one step and done… I would do a N200.
Let me explain my strategy towards upgrades. To get the very most out of an upgrade cycle you want start with a balanced system… where no one component is really inferior or greatly superior. I think you are there. Then to upgrade, you choose the first step … in this case I would guess the best step would be the preamp. Then over time bring up all the other components.
So, if you want to build a much better system over time, I think I would start by getting a high quality preamp and continue to use the amp part of your integrated amp. Then over time upgrade the amp, then front end with a good streamer.
Hopefully, you sense that this os a hard call. Small rooms can be great if you don’t get carried away with huge speakers and amps… sounds like you are thinking the right thoughts and doing the right things.
Hmm, what preamp? I would go used and save up to the 2.5K maybe. I’ll have to do some research to come up with a recommendation.