Op… “What preamp and speakers would be a substantial upgrade to your ears?”.
My ears are highly influenced by the last fifty years pursuing high end audio. At first influenced by the ethereal sound of planar speakers… while trying to maintain slam. Then many years of listening to live acoustic music and realizing I was chasing something that wasn’t real… not that this is bad. But it would make electronic music sound better, but make jazz and classical sound worse. So I turned and went the dynamic speaker route and tube electronics. The change and improvement has been profound. My system used to make me enjoy listening to my system (literally) for forty five minutes or so… now I find it hard to pull myself away after a couple hours… I listen three hours a day. It is so musical, if I want to listen to details… they are there for me… so is glorious highly detailed bass. But my system is not a bunch of details with slam.
So, to answer your question. After you put the digital end in place. Go for an audiophile grade tube preamp… Audio Research, Conrad Johnson, or VAC. Buy used… not over 10 - 15 years old. These companies not only capture the first level of musical reproduction.. but layer after layer… layers you are probably not aware of yet. Like rhythm and pace… something that took me decades to identify and realize how important it is. These preamps give your system the magic present in real music as well as including details and bass.
Speakers, I am on my third set of Sonus Faber. I have moved up the product lines after my first purchase of used. I was struck by their unique sound about twenty years ago. Over time I realized it was their uniquely natural sound that matched the real,world… and an exceptional match with Audio Research equipment… how I got to where I am.
You do not have to spend a fortune to do all this. Used equipment can be the best way into the high end. I would read a lot of reviews from The Absolute Sound, Stereophile, and HiFi+ about the equipment produced by the companies I mentioned… contemporary and older… stuff you can afford as well as at their top of the line products. It will paint a picture of companies that know what top level audiophile products should sound like and have consistently manufactured them and advanced the art.