1986 300e Becker Radio modifications?

Currently there is an Alpine 6CD player connected through FM the aerial. On some CDs (especially Beatles CDs which are known to have a higher than
normal output level) I get distortion. I may be able to attenuate the output from the CD player. Would prefer to connect at line level.
Looking for a way to add a line in and line out connection (to add a rear amplifier). This should be doable? Has anyone done this?
Many thanks SR
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