need advise, which is the weakest link in my audio chain

Nagasaki, A few suggestions:

(1) As several have already said, your  room is a box and is not optimal in dimensions. Please take the advice offered and play sound with your sound treatments

(2) Your DAC situation is confusing at best, and a great DAC is key to all of your digital audio. A great DAC that fits the exact sound signature you want would be a Denafrips Pontus II 12th Anniversary…..about $1,850 through Vinshine Audio

Unless or until your room issues can be addressed, component upgrades will most probably be money wasted.

If you’re looking to upgrade components, two things…integrated like the Pass Int60 or even Int25, and new dac plus streamer. Ditch the bryston separates, use your Marantz as a transport plus stream from Qobuz or Tidal . Keep in mind, as I said earlier, that Marantz isn’t a harsh sounding player so the amplification upgrade will make a more positive impact thsn adding a dac to those Bryston components.

yes, i agree with most of you .. room issue limited the potential of my current setup

i was so desperate to find the weakest link on my equipment until forgot my super small square box room is the one degrade the overall sound😅

btw, i am non I.T savvy guy, how to upload picture here ?

my room photo was in my computer hardisk.