Did you try adjusting the line-in sense options?

Please have a look

I didn’t get much difference when I switched between line-in sensitivity so I stuck with ‘medium’.
For pure audio, you’d be better going the 28s route. I went with the Theatre and have a couple of BL3s as rears. It took me a long time to get a sound I liked from my Beogram record player with this setup and it is still a work in progress really.
I have the Beogram (no internal phono preamp) connected to an external phono preamp, then a 1 meter decent RCA to mini Jack cable to a Beoplay M3 with volume set to 0. (The m3 Millemissen’s great idea!)  The M3 is wired to the home network and I use Beolink multiroom to play the record player through Theatre and sometimes just BL3s as I can assign speaker groups. I use BR One for volume, and Join function for multiroom.
alternatively I could use 12m of line-in cable to the Theatre but when I tried that, did not sound good.

link

(The m3 Millemissen’s great idea!) The M3 is wired to the home network and I use Beolink multiroom to play the record player

Actually the idea came from Henrik of the BOTF - maybe he even had it from a member of the BOTF. So kudos goes to Henrik….I was just the messenger. (I do this myself - with an M3 and the turntable well hidden away in a cupboard….because I seldom play vinyls. It works well, though). Login to view image MM