As I live on the 'wrong' side of a hill I need a high gain roof top antenna & booster to get DAB, there are 2 DAB radio stations I tend to listen to, Planet Rock & BBC Radio 6. Planet Rock is on DAB and broadcast in MONO! yet in stereo on the internet, but the internet version has rather more adverts for Gambling firms which annoy me! Even though I live in a poor reception area, FM reception is better, no DAB digital burbling brook sounds.
For what it's worth BBC 6 has rebroadcast the Genesis 78 show at least once, and while the audio seemed to be a little messy the encoding was still in decent-ish state. Also, XRT in chicago has broadcast at least one encoded show digitally and it seemed to be pretty well intact. Having said that, lossy sources do tend to start sounding worse and more the more you try to decode them.Yes DAB is dreadful. The UK was an early adopter and now we are stuck with this ancient technology. DAB audio is indeed encoded in MP2. It wasn't too bad to start with when there were just a small number of BBC stations operating at high bit rates, but a huge number of commercial stations have grown up over the years up occupying the available bandwidth at the expense of bit rate. A later version, DAB+, is licenced for use in the UK with aacPlus HE v2 encoding which is marginally less ghastly. However, only a small percentage of stations use it, and none of the BBC networks unfortunately. Thankfully very high quality FM is still very much the mainstay of the UK radio system.
I very much doubt anyone will have tried transmitting matrixed quad over DAB - why would they? No one under 60 has ever heard of such a thing! But I've found if you feed the low bit rate stuff into an Involve SM you can get some unpleasant burbling noises from the rear channels.