I'll be 70 this year and depending on your streaming service your current setup should sound pretty darn good. The PSAudio MK 1 is a nice DAC. I have one and it took me a ,long time to finally upgrade it. I fed mine with all the inputs USB, AES, I2S spidf and honestly while they have slight differences I couldn't walk into the room and identify the input without looking.
Trying to get your streamer the cleanist electrical signal might help. If you use dimmer light switches turn them off or all the way on. Removing any switching power supplies from the circuit and feeding the streamer with ethernet not WiFi is an easy way to optimize your sound. I haven't tried all the tweaks like running my router with a LPS or replacing the Ethernet cable with fibre but in some instances it might reduce background noise.
The biggest change to your sound without throwing money at it is to bypass the preamp and use the. DAC s volume control.