Hi Robert and welcome to Beoworld!
You need to add an RIAA Pre-Amplifier between the Beogram and the BC2300. The BM3000 would have had a built in RIAA pre-amp.
Sounds Heavenly advertise this one and will supply the correct cable adaptors: https://soundsheavenly.com/products/pre-amp-bundle-for-b-o-beogram-and-all-turntables
Or this one from OneRemote would ‘future proof’ your system because if you buy a non-RIAA remote-controllable B&O turntable in the future it would allow remote control: https://shop.oneremote.dk/shop/69068-riaa-forstaerker/121270-riaa-iii-forforstaerker/
Hi Guy and thanks for the welcome. I guessed that it would be a lack of a pre-amp that was the problem but I read that the 2300 had a built in phono amp – clearly & not surprisingly the AUX input is a line level input not a phono input. Thanks so much for the advice – I’ll get one of the above pre-amps and enjoy listening to my vinyl collection through the 2300. Cheers Rob