Hi, @Paul_Whittaker.
If I’d gotten here earlier, I might have tried to discourage you from going down the M11S (or any FiiO) path. It’s hard to recommend ARC on a DAP. It’s hard to recommend ARC at all, but I find it particularly unsuited to a DAP.
I have an M11 Plus ESS which I use as a mobile Roon endpoint in my home. It’s great at that.
Outside my home, even when I’m able to find stable WiFi, it has issues playing bit perfect, and only download to offline from my personal library, and requires occasional resets which blow away anything I’ve downloaded. My iPhone is better at ARC but even that has issues.
I worry that if you bet on ARC on an M11S working at a wedding, you’ll have issues. That would be lousy.
I honestly think your phone - Android or iPhone - is a better bet and I’d make the bet on the download capabilities of some dedicated music player like Qobuz or Apple Music. If your stuff is in Roon, Soundiiz can help you get it over to that other player, that other player will be able to offline anything, and it’s likely to be there when you need it. If you want better sound quality, get a dongle DAC. Depending on your phone, you can get a USB-C or lightning dongle. If you are going to be using the phone for a while, chain two dongles, the first of which takes power in.
With regard to the FiiO, I wrote a post of setup tips (actually several) in this thread. Maybe you’ll find something useful: