One of those forehead slap moments. I was trying to think about what might be different between the setups (except for about 3 years of RetroPie development) when I realised the cable/wifi thing. I'm glad I worked it out, because my next option was to undo the NAS and put everything on the micro-sd, but the one I'm using isn't big enough, so I'd have to get a bigger one and go through the hassle of moving everything over, etc. Glad I don't have to do that.

@EctoOne I second this, I've requested this before. It makes sense to have boxart and a screenshot option in detail view using the md_marquee. this could give people the option of displaying either static (screenshot) or video view, while still displaying the boxart. Plus - for my personal preference, i could turn off my annoying fan noise when using screenshots lol.

Yeah bro, is what I did, thanks