Compared to HD 800, on a scale of 1 -10, its HD 800 = 10 & TH 900 = 5. IMHO. But you still can't listen to TH 900 next to someone sleeping as it would disturb them. Unless they are like me, I go to sleep with my speakers playing
I am in a slightly similar situation as you. Have the HD 800 & TH 900 , waiting for T1 to be delivered.
Well if the HD800 are a 10, then the T1 would be an 11 as i find them to have a tad more leakage than the HD800. Where does the sound leak from on the TH-900? Is the ear pad seal not very tight; as far as clamp pressure?
It's not the pads - I forget the term they used, but Denon called it "sound optimizer" or something - it's that space between the cup and the pads and it's there by design. Since Foster built the Denon's and it's for all intents the same chassis, this is the leakage spot. Helps it feel more "open" and my wife can definitely hear my music when she's watching her educational reality crap TV.