In my experience, wireless connection worked perfectly unless on certain occasions when signal was weak and I was trying to listen to large WAV files (High def WAV). On those occasions there would be random signal drops.
One free thing you can always try (if you have not done already) is converting all your files to FLAC. That's because FLAC files are smaller and allow faster wireless transfer.
Without a doubt, a NAS with Ethernet wired connection is best because you are not at the mercy of a weak wireless signal not to mention the advantages of a NAS over a HDD.
All my files are FLAC as they were exported back out of the sooloos. Actually normally it’s okay but with Tidal files sometimes it drops the connection. Innuos told me the sound should be better if you use their internal SSD storage. They can then have automatic back up to a NAS which sounds good.