John Duncan said:
Ok, so it seems that surround would involve completely changing tack and would throw away what you've got in terms of Mac Mini and NAS. In which case, let's stick to stereo, and I'd suggest two things; a DAC/Headphone amp for the Senns such as a DACMagic Plus or Beresford, and a pair of KEF X300As for speaker duties, which are USB so involve the absolute minimum of faff. You should hear the X300As first as I haven't, though Mr Clough tells me they're very good.
This of course would parallel my own views, I would simply point out that the dacs you mention have good line outputs that would drive virtually any active speaker at this end of the market, so there is no absolute requirement for a digital (usb) input on the speakers. My own choice would be perhaps a little more ambitious, maybe an Audiolab Mdac and a pair of Genelec 8020 or 8030 models for example.
On the other hand, should a more conventional system system be required then perhaps a Universal player such as the Oppo mentioned above combined with a decent A/V amplifier, a Yamaha for example. Such a set up would allow you to connect pretty much anything, audio or visual and switch between them on the one unit. Plenty of people on here could offer specific recommendations, this is not my area of expertese.
With the player and amp chosen from recommended units, checking that they offer the functionality you require, then all you need to do is visit a decent dealer and audition suitable (conventional) speakers. Tell the dealer about your amp and most importantly how the speakers will fit into your room, a couple or three photos would not be a bad idea.