I would like to get my hands on a Beomaster 900, but how compatible is it with 'modern' auxilary components? Will it support my Thorens turntable? I see it has a tape recorder jack. Could I also hook up a CD player?

CD is no problem, you connect it to the tape input with a DIN-RCA -adapter (or directly if it happens to be a B&O CD with a DIN connector).

The grammophone input may have a pre-amp (depending on version), but it isn't really suited for modern magnetic pickups. You could connect the turntable to the tape input with an externall RIAA pre-amp, but then of course can't use the CD at the same time. If the particular BM900 is missing the preamp altogether (built for a ceramic pickup), the phono input might be usable as just another line level input.

If you re running out of inputs you can but a box on ebay that will anable you to connect a CD player and a truntable to a single Phono input ans switch between them. It's an ugly plasctic  box bit can be tucked away out of sight.

Simon