Your problem sounds strange to me. I'm using a Cat5-wired LAN, 100Mb. Between the NAS and the Sonos Connect LAN-to-audio streamer there are 20 m+ cable, 2 switches and a router. No problem whatsoever to stream .wav files (or .mp3), no glitches. Only very very rarely when I dump a large file to another NAS on the same LAN - and that I would expect.
So, maybe it's something else: cableing, poor switch, heavy LAN -traffic, ..... Make a drawing and identify all potential troublespots. Good luck and nice listening!
Jan