New here - Eclipse 4421 to external mp3 player?

Hi everyone,

I'm new here and trying to breath new life into my Eclipse head unit model 4421. its about 14 years old and has always sounded awesome even with my stock Ford ranger speakers! the cd player failed years ago (hmm, right after the 3 year warranty expired) and more recently the cassette player is making noises and not playing both sides of tapes well. and since the tape deck is malfunctioning, the use of a cassette audio adapter for my mp3 player is out of the question. I feel RF adapters are a pain, they need batteries or a plug in power source and the sound quality is poor. I was wondering if there is a way to use the din cable from the external cd changer and modify it so i can use it to connect an mp3 player. has anyone attempted this kind of hack?

also looking for new speakers (and maybe even a sub)to finally take advantage of what that 4x35w HU is capable of. I've heard good things about speakers from eclipse, infinity and pioneer premier. i believe i can use 5-1/4" or 5x7's in my 93 ranger. Does any one have particular favorites? Also should i prioritize replacing the front door speaker pair or the the pair behind my seats? the ones behind the seats sound flat and muffled whereas the door speakers sound decent, so i feel i should prioritize the rear channels first. but then i think i should replace the speakers that are more exposed and in fron of me for best effect. Curious to here peoples thoughts on that as well.
thanks!