Think more than just the dacs. Look at the design and implementation.I am glad to hear you say that the Fiio sounds better because after replying to you I found the DP-X1A available for £439.00 and I was thinking of buying one.
Do you believe the difference is due to the chosen DACS?
I notice that Onkyo and others use the Sabre DACS whereas Fiio uses the same DAC found in Astell & Kern.
It's designed very well so that very little noise interference from CPU doesn't easily reach DAC/AMP section