Superb review as always, thank you! Wondering why you gave it 4.5 stars vs. the 5 stars for the Senn HD 650. Is that because (technical issues aside), it's more uneven in sound quality? I'm referring here specifically to the distant mids which you noted. 

Nice review. Sorry to hear about what happened to your DT 990 600 ohms. The DT 990 Pro was my first experience with a Beyer, it has always been a love hate relationship with the headphone, loved it's cleanness but always had issues with the treble spike it had. Though I will have to say the Beyer drivers and biocellulose drivers are completely different animals, they have quite different sound characteristics, look completely different, etc. They did come about for similar reasons though. The Beyer drivers truly are exceptionally clean and break-up free. There is only one complaint I really have about Beyers sonically, but it doesn't really have anything to do with their fidelity. They seem to have some trouble portraying the emotion and euphony in music to me personally. 

@Willy 2 Streams

Thank You, Sir!
I gave it those ratings because of the very common defective driver problem I've noticed with Beyerdynamics, even the T1 faces these assembly line defects from time to time.

@kman1211

You know Kevin, I'll not disagree with you on the emotion and euphony part.
But at the same time very few can portray what you want.
I lost respect for Dynamics and their ability to be musical and still retain top tier fidelity after hearing the HE-60. The only headphone that could touch the HE60 and beat it in some ways was the DT48.
I think modern Summit-Fi Dynamics have reached an impasse, at least for me. 
 

That is true about most dynamics, some are more euphoric than others. I find the HD 650 more full of emotion than most Beyers, same with certain AKGs, but I'm not saying Beyers are bad at it, just not quite to my liking in that aspect but I realized most headphones aren't. I find even some electrostats and orthos have that problem as well. The Senn electrostats are unusually musical and euphoric. The most euphoric headphones I've ever heard were the R10 and the Orpheus, everything else I heard seems to lack emotion. I find it's often the older models of headphones that seem to be the most euphoric. I found the HD 800 one of the worst offenders in terms of lack of euphony with summit-if dynamics, it's too sterile sounding. The T1 and K812 at least have some semblance of musicality and euphony.

I'm not really sure what direction to upgrade anymore, maybe I should simply stick with what I have, the HD 650(got because the HD 600 wasn't quite what I wanted and I really appreciate the extra refinement and euphony of the HD 650), DT 150, and K712. I got myself a K240 Sextett out of curiosity, I hope the fidelity is good, but I really hope it's very euphoric like people say it is, while the a K240 Studio/MKII were euphoric that ragged treble drove me nuts.

Excellent Review

I was under the impression that running a can balanced, you would have to have separate connection to each driver. What is the point of modding them with XLR if you are not running them balanced?

@ayaflo

Thank You, Sir!

To your question, here are the few reasons I went 3-Pin Unbalanced.

1) I don't have a balanced system.
2) My 4-Pins were all gone, only had 3-Pins in stock.
3) Didn't have 4-Pin Females.
4) The 4 Pins Fs I had were cheap "Made In China" one's with fragile contacts. My Amphenol one's were all gone as I said.

Since the XLR was fastened via Nuts and not Epoxy or Hot Glue, I could easily swap them out and go balanced, single sided.
The routed wires are very long to reach the XLR, this way I can have the convenience of a single sided cable and also be balanced.
Although this wouldn't matter now because if I had gone balanced, I would just go dual XLR to keep my OCD at rest and most importantly it doesn't matter because my 600Ohms are no more!

Let me know, if you need more.... 

@kman1211

Sextett, very nice!
I found a extremely old and molested DF in India, it was in an unimaginable shape. Restoring was not worth it, so I let it go..
But I do want a Sextett and K280.

Thanks. I couldn't get a good look at the radiators at whether they were orange or white. It seemed in very good condition by the pictures, cable and connector seemed pristine and there are only a couple minor scuffs and mild wear on the AKG lettering on the headband. The solid headband seems to indicate it's either mid-production or late-production. I'll probably be posting impressions in the Sextett thread, really curious how it stacks up with my headphones, say if it can keep up or if it's below them fidelity wise. Wish you luck on finding either the Sextett or K280 in good condition so restoration isn't necessary. 

superb review. Wish you all the best on your German tour. hope to see some pics of the factory ( if they allow to take pics )
 
anyway I got some questions if you don't mind,
do you also find 880 600ohm is higher fidelity over 880pro too?
any chance you can review MT220 soon?
 
thanks.

@appsmarsterx

I do find the 600Ohm DT880 to be better, just adding smoothness to the tone. Also the 600Ohm has more Mid-Range.
My 600Ohm DT880 is a very rare PRO hence it has more Sub-Bass than PREs and also has a slightly more pronounced top end as well. The DT990 600Ohm treble is perhaps the highest fidelity of all DT headphones.

Thanks for the info. btw I heard Beyerdynamic are making the drivers for the MT220, that's why asked you to review it. It is now on sale for $150 on amazon these days, not sure to pull the trigger or not. earlier I was thinking about getting a dt150.