Distinctly Digital Forever?

So, just to further my understanding: assuming price no object, does there exist any DAC, or DAC/Pre combo, capable of making my streamer (or the best streamer in existence, for that matter) sound indistinguishable from an FM radio signal,

That FM radio signal comes from a digital source at a low bit rate and is compressed/limited to boot. So, if you’re only getting FM quality from your digital gear, something’s wrong. It should be very easy to better an FM radio signal. There are people who prefer low bit rate music into ear buds over CD quality or hi-res digital on a good system, though.

Something always made me believe that a decent tube preamp could "mellow" or "naturalize" the sound of digital sources.

Dgital sources can sound natural and even mellow, if that’s what you want. I prefer just natural and there are many choices for that.

If your digital is sounding harsh or bright, you’ve got the wrong player.  What CD player or DAC are you using?

hickamore, Why not just listen to FM and vinyl if that's what you like?  it's unlikely that someone on a forum will come up with the DAC that's going to give you the exact sound you want in your system given all the variables.  You'll get a lot of suggestions but you won't know till you bring one home and try it. 

If you don't have access to the millions of albums available through streaming that way, well, life's a bitch.