From what I've just watched and read the Topping D10S (specifically the updated newer model which you have) is a very well regarded £100 DAC with a very clean output. It's a pure DAC with no controls for taking USB input and converting it into COXA, RCA and optical out to any AMP(s). What you 'might' be missing is the AMP.
One thing I understood is that headphone AMPs are generally considered better than HiFi AMPs for headphone use, and this is where it feels to me like you almost have separate requirements; to drive the AKG K702's, or any other headphones you use, and drive the KEF Q100 passive speakers. Something like the iFi Zen Can or Topping L30 AMP (working with your D10S) is going to do the former well, but not so much the latter. Hence my very early comments in this thread that the X7 was doing a lot in one box.
However as mentioned did you have the SBX features enabled on the X7?