I cant really say personally what the Qualia is like as its one of the few top headphones i've never owned or heard. I think someone else on this forum might have owned a set. I would be surprised if it has the same sort of tonality as the O2. In my experience I have not heard anything much that can rival the overall attributes of the 02 (except another Stax or electrostatic). However; some dynamics can do things in different ways to the 02 that IMHO still make them worth listening to, even though they may be flawed in different ways.
Many people go for dynamics over electrostatics for the supposed superior bass and on first hearing yes it has impact, sounds full, and prominent, but on closer and extened listening its really an illusion. Spritzer sums it up well as "one note bass", and the more you listen you realiase that the bass on many dynamics is not that articulate, and you really cant differentiate the bass line and textures that well, unlike the 02. The headphone that has impressed me recently in this respect is the Audeze LCD-2, really articulate tuneful bass, and to my ears similar tonality to the O2. However; I still feel the 02 is superior overall.
Here is the link to the RKV My link. Produced in Germany they dont appear on the market that often so you might have to wait a while before one turns up. They appear to be more plentiful in Europe than the US and as far as I can remember I paid about €600 used. The one I had was best I feel with the telefunken tubes, but as the K1K needs a lot of current sometimes on big transients I felt it was underpowered. The K1K is better with something about 10 to 15 watts into 8 Ohms, more like a good speaker amp. I have a friend who uses an ASR Emitter 280 watts into 8 ohms for his K1K's.
I would love to build some of Kevin's designs but just don't have the time as I dont know where i'll be working from one month to the next. Perhaps a hobby for when I retire (if ever I can afford to)