The “B&O Way” is to connect the turntable to the Moment. It has auto-sense and should turn on and select the source automatically. Then by virtue of Beolink Multiroom, you can tap (or long-press?) on the ring of the A9 to join the playing Moment (as you probably already know). Although the A9 also has a line-in, it might be less convenient to place the turntable and run longer cables.
Either requires RCA jack line-in connections, which means you need a turntable with (1) RCA male cable output, and (2) pre-amplified (“line level”) output. Each of (1) and (2) can be accomplished by purchasing a turntable which has already been modified or configured for it, or can be accomplished with external cable (DIN female to 2xRCA male) and external phono RIAA/amplifier box. Choice of turntable is determined by not only those requirements but also longevity/repair issues, both of which — hopefully — others will comment upon, below…
