Good question. I always upgrade in steps to a plateau, enjoy until I am ready to get started on the next level.
In general, your equipment looks to be pretty compatible and on the same level, so there are a couple ways to go.
My rule of thumb is always upgrade a minimum of 2x in cost... so once you start, you want to slowly upgrade until you have all compatible equipment at that level.
Since it sounds like are going to be looking for better sound over the long term... make each new component at that new level.
Step one: Flesh out this level. As mentioned above get a high quality power conditioner. While it is remotely possible you have great power, most likely not. Get a good one so you don’t have to rebuy for a decade.
Also, get a high quality streamer. You get nearly infinite music for the price of a CD per month with as good or better sound than red book CD. Think used Aurender or Auralic... not just a Bluesound.
Step 2: This would be to start moving the whole system up a level.
1. Speakers used are fine go 2x or better 3x original cost... this will put your system in a whole new category.
2. DAC ... be carefull. You have a very warm one. This might be a tricky transition, but worthy of making.
I would imagine this would take a couple years. Then upgrade cables and interconnects, power cords and tweak. Enjoy for a few years before the bug bites again.