Great little speakers, had the Zensor 3-s some years ago - loved them. So I dont think you can get a pair of active speakers for that money that would be better.
Personally would go for the DAC solution, since the Marantz is a decent amp and you cant get a better amp for that money, especially with a built in DAC
They all offer digital and analog outputs, so you can use it as a DAC temporarily and after change for a better source. The Fiio has USB/coax/spdif in also. Just can’t say about how good the internal DAC is, but I guess it’s something. The only thing is I don’t know if you can find them in amazon uk, but you at least can get them form China.
What did you end up getting? I’m considering a Bluetooth DAC to replace my FiiO E10K because I want to be able to easily switch everything from my PC to my work laptop when working from home. I’ve started a true wireless revolution at my desk, haven’t figured out what to do with my e10k and liquid spark though.
I’m considering getting a Xduoo XQ-50 or SMSL B1 or something, as long as it’s as good as the e10k as a DAC and has Bluetooth I’d be content.