Hey... I forgot... and I did do a back to back comparison of Siemens CCa's to the Siemens you sent... (can't remember which type)
In a nutshell from what I recall, the CCa's were better in every way... more bass extension, sweeter highs, and a liquid midrange. The CCa is a great tube choice for the DK.
The Siemens you sent weren't bad but they rolled off the highs more than I like and the bass didn't have as much impact. The midrange was still smooth and enjoyable... in fact, despite being dwarfed by the capabilities of the CCa's, it's a good tube... better than some, not as good as others.. and may do the trick for your particular gear. It's a flavor.
I ended up going back to my rocket logo Russian tubes in the DK. It's the flavor I like today.

I've used Amperex Gold Pins (the ones with 'PQ' on them with some success also in the DK. They do nothing 'wrong' but they do nothing for me either. It's probably the most neutral tube I've tried.
So, that's my long overdue review...
Thanks,
Carl