Below are recommendations for subwoofers (you should get two), a DAC, and a room correction device. With two subs the total would be about $3350. You don’t need a preamp as you’ve already got a nice integrated amp.
https://www.svsound.com/products/sb-1000-pro-subwoofer
https://www.ebay.com/itm/285086265679
As an alternative you could get this DAC, which is also excellent (I own it), and save $875…
https://www.usaudiomart.com/details/649937157-musician-audio-pegasus-balanced-r2r-dac/
I’d think incorporating these things would bring your system to another level entirely. Go with Qobuz and forget the MQA nonsense. Hope this helps, and best of luck.