Nothing can replace a room/speakers acoustic optimization, certainly not an upgrade in dac... nowadays, i know it by experience, dac technology is mature...The problem is picking a dac with a good synergetical complementarity with the amplifier and the speakers or headphones...
I spoke about MAJOR improvement with acoustic here not marginal improvement going from one good dac to another good one...
The equivalence between room/speakers is an headphone with a relation between the driver and the shell cup well designed....
Most headphones are not acoustically well designed, at least the 9 headphones which are all under my bed nowi owned...
The tenth was a marvel but very hard to optimize it takes me 6 months of listening experiments and modifications around it or inside it and it was necessary to figure out how to listen to them, because we must learn how to listen to speakers or headphone if we want to optimize them acoustically... Akg K340 hybrid is my ONLY choice now... Upgrading is unnecessary for me...