I'm on the same boat with you.
I'm a big audiophile myself (regular member of HeadFi) and sound quality via 3.5mm to me was the biggest disappointment. Loved Lumia 800 otherwise.
This goes hand on hand with the camera performance of the first Lumia series. Nokia is known for stellar, if not of the best sound quality via 3.5mm on N8 and 808 PureView and Symbian phones in general, but delivered something absolutely different to Lumia line of phones. As a owner of 808 PV the sound quality to my customs and Denon's in-ears is best i have ever had on a portable device. GSMarena has also put top marks on 808 on their true testing system.
Nokia 808 PureView review: Photo Finnish - GSMArena.com
Lumia 920 at least looks to be so more stellar performer with hopefully more mature OS. Dolby Digital Plus itself for pure music enjoyment doesn't mean much but it could mean that Nokia has put way more thought on that audio department than they did on Lumia 800.
Only time will tell. I got enough trust on them with Lumia 920 that i will have the phone in release date.