NAS / Sonos / PS3 streaming issues

This is perhaps more of a networking question than specifically Sonos but there are some knowledgeable posters here so I hope it's OK to ask this.

I have a simple home network with a NAS streaming video to a PS3, and music to a couple of Sonos players. Since adding the Sonos players, streaming video to the PS3 seems to have suffered - it's more juddery and sometimes I lose audio. Also occasionally the music streaming to the Sonos players cuts out.

The PS3 and Play:5 are wired directly to my router (Virgin SuperHub) and the NAS is wired via powerline adapters to the router. It's not a long hop (NAS and router are in adjacent rooms) and this used to work fine. I also have a Play:3 with no wired connection.

Is it likely that adding the Sonos players to the home network has somehow upset the streaming to the PS3? The issues I'm having occur when both Sonos players are inactive, so I wouldn't have thought it was just a bandwidth issue.

Could it be the somewhat infamous "quality" of the Virgin SuperHub router? Are there any settings I can change on it, or would setting it to Modem Mode and buying a new router help?

How do I troubleshoot these network issues?

Thanks!