Mercedes W123 300D Stereo?

[William727]

I own a 1978 Mercedes W123 300D and would like to get some descent sound out of it. The whole system is stock, and after 32 years the speakers are a bit average. I would love to put some modern speakers in but would not like to change the original head unit, is it possible to use a an amp that does not use an RCA cable? Also what other options do i have?

Thanks