Keep all your connections digital and quality loss isn't an issue.
Hell, you're talking about Spotify which is already madly compressed - not sure there's any "quality" to be lost
To be honest, at your budget everything is going to be much for muchness and will likely come down to your speakers. Which, at the price of a Marantz PM6005 looking to be around £280 mark you'll probably be looking at £150/£200 mark for a nice pair of speakers to match.
If you're wanting to go down the pure streaming audio route without doing the AVR option then I'd seriously consider a SONOS as the Play 5 will cost less overall and likely fit all your current needs while being totally extendable to the rest of your home.
The online rainforest has them for £342 and with Prime you'll get it tomorrow. Job done.