Hi Charles,
I had come across this while trying to find a good comparison of the v6 classic vs vivid. I just recently acquired a pair of hifiman he-4xx phones and have them paired with a little dot 1+. I have started tube rolling and currently have upgraded the stock tubes to Voshkod 6ZH1P-EV with some Mullard 8100 on the way to try next. I am pretty new to this game but researching opamp rolling on the littledot 1+ seems to be another step in the adventure. If you have any recommendation as to which would compliment the setup best I would welcome your opinion. I think the tubes give some warmth and texture, so I was leaning towards the vivid. There were some older reviews of the Littledot 1+ with the V5, and while it didn't fit with the cover closed, it sounded like it was an amazing upgrade over stock. I am not opposed to milling out the aluminum case to fit taller opamps.
It looks like the stock opamp is an MC33078N
https://i.imgur.com/WNI9BrE.jpg
Little Dot exposed
https://i.imgur.com/M1f4bSd.jpg
Gratuitous glow shot
https://i.imgur.com/YtYOst6.jpg