As you obviously enjoy tube and analog sound, I'd recommend the Mhdt Labs Orchid R2R NOS DAC. Cost $1100 sold through Linear Tube Audio. I'd contact them and ask about their return policy to see if you can do an in-home demo. I think your system will reveal significant differences between this and your Yamaha. Here's a recent review on 6moons...
https://6moons.com/audioreview_articles/mhdtlab/
If you don't have a digital cable, I'd highly recommend starting with this one as it's very good and very cheap. You'll need some burn-in time and pay attention to directional arrows.
https://www.amazon.com/Geistnotes-Apogee-Wyde-Cable-WE-RR/dp/B01N29180M/ref=sr_1_1?crid=CE67OLG5CU63...
Best of luck in your digital journey.
https://6moons.com/audioreview_articles/mhdtlab/
If you don't have a digital cable, I'd highly recommend starting with this one as it's very good and very cheap. You'll need some burn-in time and pay attention to directional arrows.
https://www.amazon.com/Geistnotes-Apogee-Wyde-Cable-WE-RR/dp/B01N29180M/ref=sr_1_1?crid=CE67OLG5CU63...
Best of luck in your digital journey.