I also thought of putting together a second system at this price point.
One simple solution would be to get good powered monitors and a 100€ DAC with a remote.
The Kali LP-6 v2 seem to be the best option in this price range.
Another option would be getting a good amp (like the new TPA and Infineon stuff) and getting a pair of good speakers from eBay.
There are plenty of speakers from the 80s and 90s which are really high end and can be found for a few hundred bucks used.
You can get surround speakers and a surround receiver later. Focussing on good L+R speakers is more important