Do you actually have the 39, or are you considering buying it depending upon it’s headphone performance?
The headphone performance of the DM37 wasn’t it’s greatest attribute to my ears, but two models down the line things may have moved on. Now there are a couple of variables involved here, but I’m hoping to go and listen to the new 39 at the end of next week with a view to purchase depending upon how I feel about a particular issue with the previous two models. If I do buy it then I will then gladly give you an opinion on how I think it performs.
Alternatively, if you’re not a million miles from a RS then go and have a listen for yourself. I would assume that they would have the 39 on demo and they do demo headphones (at least the one in Birmingham does), although RS don’t stock Beyer.
EDIT:
I’ve just noticed you’ve asked on the 39 review how it’s headphone performance might compare with the CD6004 which is going to be an unfair comparison.
It will be a lot "better" with high impedance cans for no other reason that it’s got the grunt to drive them properly, but a dedicated £300 CDP is going to bring up a whole lot more detail and instrument seperation than the Denon can deliver. Enjoy the Denon for what it is – I loved mine!