Goat, I will repeat, to retest your KEF/Arcam, get a good CD player and bypass your Marantz completely. Contrary to the opinion here, 11 years ago my experience was that a then new Pioneer DVD player was rubbish compared to my then already 11 year old budget Technics CDP!
Note too, that if it is the Marantz at fault - it won't be down to the DAC alone, but could be down to numerous factors in the streamer's design.
Forget your Tosh, temporarily forget your Marantz, get to the nearest dealer and steal a good CD player for a weekend to determine if it's really your amp/speaker combo.
And if it's still horrid, then think about a change...
Arcam Solo Mini/Monitor Audio RX1/Cambridge Audio 751BD/Samsung 37” LCD
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