I’m not familiar with this unit. In general you can connect older units by pretending that the SONOS Line-In is a cassette recorder. The output terminal on the old unit is often labeled “REC OUT” or “TAPE OUT”.

As suggested, any device with a normal line level output will easily feed a Sonos line in. Troubles occur with Phono level inputs from turntables (insert a pre-amp) and variable volume inputs, such as from a headphone output jack (start at 50% volume first, then adjust). 

Thank you for you help. Just looking at the line plugs on the back (see photo), there is a phono in and then a DAT/VCR PB and Rec. Do you think I could take a feed from the DAT/VCR Rec plugs? Sorry if I am asking dumb questions

From the PB side, which I suspect stands for Play Back, yes. The other ones, marked ‘Phono’ and ‘Rec’ are inputs, not outputs. No preamp would be needed.