Lack of depth problem

I don't think you need tube traps on the ceiling, Vett. I just like to experiment, having had tube traps since 1988 and still find them great for absorbing bass.
If you have any "jogs" in the room, bass does tend to pile up there. That jog in my room from 13' to 12'8" was piling up quite a bit, something I didn't realize for many, many months. Otherwise, just a couple in whichever corners you can put them in should smooth out any humps in the bass. It's also helpful (but only it it's not overly expensive) to have a height of 6' on the traps, which means 2 of them. I have found that the closer to the ceiling you get, the more the sound improves. I put a box in between my bottom and top trap just to see if it improved,and it seems that higher up is better! You can always try the Real Traps, but it sounds as though you have enough damping for higher frequencies, which are, as I recall, pretty short. I think a 1khz wave is 1" long -- or shorter, so I wouldn't worry about that too much. One could have a tall ficus tree to break up those wavelengths. It's the upper bass that I find haunts most rooms of normal size.

Speaking of bass: depending on where those subwoofers are in relation to the mains- a time shift can screw up your sound stage also. There's a lot a ambience info in the bottom octaves. Try moving them into alignment with the mains as an experiment.

The coupling caps in the NP100 are Jensen oil caps and have been there for 6 months. So I think they should have broken in already. V-caps do take a long time to break in. I have a pair of V-caps in my 300B SET amp and they took 400 hours to break in. The first 200 hours were simply horrible....

I'll test my other tube amp over the weekend. One subwoofer is at an right angle to a speaker. I'll adjust it too and see (or hear) how it sounds.

I'll also keep moving the speakers forward and increasing the toe in.

The power cord for my NP100 is already a VH Flavor-4 PC! It is a fine power cord. It replaced a Shunyata Copperhead PC, which rolled off on the highs. Maybe I should put it back as a PEQ that Shadorne suggested?

This high-end audio hobby is expensive but interesting. There are so many things to learn! I built my first radio more than 30 years ago and built many amps as a teenager. At that time, I played violin, guitar, and trumpet. So I have pretty good ears for music. Then I went to college and got all my degrees in EE. But I am still learning many new things. Thanks everyone for sharing your experiences.

What a useful and interesting thread, a lot of info here for us all. I would only add, that in my experience, amps and source are very important. Specifically, digital lacks depth except from the best players. That for me is partly why it lacks musicality. Vinyl has great depth, particularly on good recordings. I have some Wagner where the chorus sounds like it is in the next street. For me also, as others have said, good tube amps with good output transformers, also have depth. Again, for me, that is partly why I prefer them.

I have some Wagner where the chorus sounds like it is in the next street

good tube amps with good output transformers, also have depth.

Good point - the output transformer coupled with speaker impedance variation with frequency will generally have a marked audible impact on the SPL with frequency - this can change the soundstage depth much in the way the mix engineer applies EQ to individual instruments to get a desired depth. Bear in mind that the mix engineer will also play with reverb - stuff that is placed far back will have more reverb added and highs cut - stuff that is forward in the mix will have no reverb (like vocalist or lead guitar) and an upper midrange/treble boost.