shouldn't be too hard to hookup a classic analog output portable CD player to one of those analog to Bluetooth converters...
I presume that's better than the FM modulator method.
Yes, but try finding a bluetooth transmitter that actually works with a tesla. Tons of those devices on amazon or ebay or alibaba or whatever, but only a few of them actually can transmit to a tesla, and the few that work require more than a little fiddling every single time you want to connect, so much so that one (at least me) gives up pretty fast. A cheapo usb or a phone bluetooth connection works 1000 times better.
Way back when I got my model 3 (3 years ago), the USB system didn't work hardly at all, so I was determined to find one of these transmitters to play a DAP with. The first one didn't work at all, so I got a newer upgraded model, which also didn't work (BTW all of these were confirmed working with other devices, just not with the tesla). So I got on kind of a spree on amazon, and bought about 6 more of these of varying prices and capabilities. Most also didn't work. I did find one that worked, however, every time you wanted to use it, you had to turn the device on in receive mode, connect it as if it were he first time (the car would not remember it), and then connect your device, power it on and start playing something, then you could switch it to transmit mode, and sometimes it would work. If you had your device connected before switching it on or not playing it wouldn't work and you'd have to do the whole thing again. I tried getting used to all that for about a week, but it was extremely frustrating and I quickly went to streaming stuff from the phone. They got the USB system working, sort of, maybe 6 months later.
BTW as I mentioned - this experience is from nearly 3 years ago - things may have changed since then. If anyone knows of a viable bluetooth transmitter solution that works easily reliably, let us know!