@milhomes Welcome to the thread.
Hope others also post responses to your questions.
1. I recommend you consider the V2 driver given your focus on Rock Music. They go a bit lower and are easier to pair with a wider array of amps. Solid state amps may be easier to pair and may work more favorably in meeting your preferences with the rock genre. Your prior reference will be a factor.
Placement is easy enough to experiment with...go with what works best for your room and your preferences.
2. I have not had any of the other speakers you are considering in my own room. They are all well implemented designs and have great owner and reviewer feedback AND will likely meet your needs. They will be different, given their design, than Cube Audio's Nenuphar.
I have heard the Rockport Cygnus in a friend's system. He's down the street from me. If you heard his system and mine, back to back, you might be very surprised by what's possible from a single driver speaker.
3. Both are 10 inch full range drivers. The Nenuphars use the top of the line F10 Neo; the Jazzon uses the F10 Select. There is a significant price difference between the two drivers.
4. The V2 is slightly less efficient than the V1 driver. Unless you are using very low output power single ended amplifiers, I do not see you running into any issues driving the V2s. Reach out to Grzegorz at Cube Audio for more specifics. The quality of the amp is a significant factor here, much more than the output rating.
5. I don't know where the F15 Neo effort is, currently. Another question worth asking Grzegorz. I have heard whispers of a flagship effort at a higher price point than the Nenuphars.
Let us know if you have other questions. All the best.