You can use headphones on all 3 of your mobile options but the FiiO M11 can also be a DAC and output Line Level (LO) on the FiiO and connected via WiFi or direct USB to your iMac. This would give you a better option using a 3.5mm to RCA cable from the M11 to your preamp
I use my iMac as a core and Mojo as DAC to my active desktop speakers and it works fine.
An iPhone or iPad can be a Roon endpoint (instead of using them as controllers).
I’ve used an iPhone that way, connected via lightning-to-USB cable directly to the USB-A port on my integrated amp (a Peachtree Nova 150, which has “DyNEC” noise-cancellation circuitry to support iOS devices). This makes for an elegant set up (small footprint, built-in screen, minimal cabling). The SQ is quite good, too (with the Nova, anyway). YMMV.
The iPad has a bigger footprint. You can’t just put it in your pocket when you travel (unless it’s a Mini or your pockets are really huge). On the other hand, it gives you a bigger screen. Otherwise, I’d expect approximately the same SQ (all else being equal.)