I have a very similar system now with a miniDSP DDRC-24 into an XTZ A2-300 power amp with Wharfedale Evo 4.3s.
Have simplified a lot lately with a preamp, streamer and probably the DAC going to be sold in favour of the Chromecast Audio direct into the minidsp.
I did get a subwoofer and I'd recommend it. Just started making Dirac adjustments having done EQ via REW and the minidsp until recently.
Nice - great system for the money isn't it. I'm planning on adding a SVS SB 1000 pro sub once I've got the cash.
Chromecast audio is a good shout actually, forgot about that. Would like to use Tidal app natively and bypass volumio. Is the audio quality up to scratch when using the optical output?