Again, you forget he's also remixing. That changes the whole game. You may be right if re-encoding was all he does, but it isn't.
You take the 256kbps high quality AAC, and you time stretch and repitch it by a few percent (to match it up with the track you're mixing it into) and probably fiddle the equalizer a bit, to "drop the bass" :)
If you do that a few times, you're losing information, even on a lossless digital medium.
If you use even high quality audiocodecs in between, it will sound like crap. And not the kind of super subtle near-impossible to hear difference between lossless and 256kbps AAC crap, but actual crap. I know this from experience myself as well. The sound becomes really flat, hard to describe, but you notice it when you're playing one right next to another track that hasn't been through such a process. It's like you want to turn it up louder but it's already loud enough. Hard to describe, but it's a real problem if you're playing these mixes on high quality speakers in a club--suddenly the sound is not as crisp anymore, and the crowd notices it too.
If you want to make the analogy with JPEG, imagine re-encoding at 95% quality, but with a few percent scaling and a few degrees rotation in between, before saving again as 95% quality JPEG.
You do that twice, with a quality high res digital photograph, and you're going to wind up with a photo that looks pretty much like the original ... until you make a high res print of it (or zoom in on the screen). Edges that were crisp at first have gone fuzzy, and at places you can spot the typical blocking and ringing JPEG artefacts.
You'd probably get away with it, most of the time, too. But not always, and if you're a digital graphics professional, this is your craft, and the mark of a good craftsman is that they put in the work for the little details that you don't really notice, until they're not there, and how you tell you're holding a piece of quality work.
You take the 256kbps high quality AAC, and you time stretch and repitch it by a few percent (to match it up with the track you're mixing it into) and probably fiddle the equalizer a bit, to "drop the bass" :)
If you do that a few times, you're losing information, even on a lossless digital medium.
If you use even high quality audiocodecs in between, it will sound like crap. And not the kind of super subtle near-impossible to hear difference between lossless and 256kbps AAC crap, but actual crap. I know this from experience myself as well. The sound becomes really flat, hard to describe, but you notice it when you're playing one right next to another track that hasn't been through such a process. It's like you want to turn it up louder but it's already loud enough. Hard to describe, but it's a real problem if you're playing these mixes on high quality speakers in a club--suddenly the sound is not as crisp anymore, and the crowd notices it too.
If you want to make the analogy with JPEG, imagine re-encoding at 95% quality, but with a few percent scaling and a few degrees rotation in between, before saving again as 95% quality JPEG.
You do that twice, with a quality high res digital photograph, and you're going to wind up with a photo that looks pretty much like the original ... until you make a high res print of it (or zoom in on the screen). Edges that were crisp at first have gone fuzzy, and at places you can spot the typical blocking and ringing JPEG artefacts.
You'd probably get away with it, most of the time, too. But not always, and if you're a digital graphics professional, this is your craft, and the mark of a good craftsman is that they put in the work for the little details that you don't really notice, until they're not there, and how you tell you're holding a piece of quality work.