Given the speaker quality and you like them. Probably the DAC… it will improve the transport sound quality and set you up when you do go to streaming… today streaming can equal or exceed the SQ of a transport.
Long term improving systems are typically done by choosing the first component that will give you a big boost… and upgrade it to the next level… then bring up the other components. So first DAC, then integrated amp ~$10K new… Streamer ~$5K… then your system would be at a whole new level, taking advantage of your speakers. Assuming each choice carefully made.