MP3 is not the greatest sounding format, but it is fine for in the car, especially if the music was free. The factory sound system in my car is fairly decent, but most MP3 music of a decent bit-rate still sounds good enough. Music I really like I'll buy on CD, but I don't use commercial CDs in my car anyway, they are strictly for use at home. I'll make a copy of them to put in the car, because that environment is not favorable for keeping CDs pristine. I do have a small SACD collection at home, and yes, they sound amazing compared to regular CD.
Rotel, eh? Nice. I used to buy and sell vintage stereo equipment as a side business on eBay back in the early 2000's, had all kinds of high end audio equipment from the 70's and 80's come and go through my home - I would test them out in a separate vintage system setup for a short while and then sell them off when I would get other vintage equipment in. Still have a few pieces left over at home, including a 1974 Marantz 4270 quadraphonic receiver, some Carver amps, a few pairs of Large Advent speakers, and a pair of Infinity Quantum 5 speakers.